The problem with your input is that the information it carries is not structured as XML. In fact, most of it is not structured at all - it's just HTML payload riding in an XML wrapper. This makes it very difficult to extract individual data elements.
To provide you with a starting point, consider the following stylesheet:
XSLT 1.0
<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:atom="http://www.w3.org/2005/Atom"
exclude-result-prefixes="atom">
<xsl:output method="xml" version="1.0" encoding="UTF-8" indent="yes"/>
<xsl:template match="/">
<items>
<xsl:for-each select="//atom:entry">
<item>
<title>
<xsl:value-of select="atom:title"/>
</title>
<when>
<xsl:value-of select="substring-before(substring-after(atom:content, 'When: '), '<br />')" />
</when>
<where>
<xsl:value-of select="substring-before(substring-after(atom:content, 'Where: '), '<br />')" />
</where>
</item>
</xsl:for-each>
</items>
</xsl:template>
</xsl:stylesheet>
When applied to the following example input (which is basically your example response, after correcting a missing closing tag!):
<?xml version="1.0" encoding="UTF-8"?>
<feed xmlns="http://www.w3.org/2005/Atom" xmlns:openSearch="http://a9.com/-/spec/opensearchrss/1.0/" xmlns:gCal="http://schemas.google.com/gCal/2005">
<id>http://www.google.com/calendar/feeds/cqdcu7b550jienqk97ddrdfhpc%40group.calendar.google.com/public/basic</id>
<updated>2015-02-24T23:02:37.000Z</updated>
<category scheme="http://schemas.google.com/g/2005#kind" term="http://schemas.google.com/g/2005#event"/>
<title type="text">SB Meetings</title>
<subtitle type="text">SB Meetings</subtitle>
<link rel="alternate" type="text/html" href="https://www.google.com/calendar/embed?src=cqdcu7b550jienqk97ddrdfhpc%40group.calendar.google.com"/>
<link rel="http://schemas.google.com/g/2005#feed" type="application/atom+xml" href="https://www.google.com/calendar/feeds/cqdcu7b550jienqk97ddrdfhpc%40group.calendar.google.com/public/basic"/>
<link rel="http://schemas.google.com/g/2005#batch" type="application/atom+xml" href="https://www.google.com/calendar/feeds/cqdcu7b550jienqk97ddrdfhpc%40group.calendar.google.com/public/basic/batch"/>
<link rel="self" type="application/atom+xml" href="https://www.google.com/calendar/feeds/cqdcu7b550jienqk97ddrdfhpc%40group.calendar.google.com/public/basic?max-results=25"/>
<link rel="next" type="application/atom+xml" href="https://www.google.com/calendar/feeds/cqdcu7b550jienqk97ddrdfhpc%40group.calendar.google.com/public/basic?start-index=26&max-results=25"/>
<author>
<name>xx.xx@gmail.com</name>
<email>xx.xx@gmail.com</email>
</author>
<generator version="1.0" uri="http://www.google.com/calendar">Google Calendar</generator>
<openSearch:totalResults>848</openSearch:totalResults>
<openSearch:startIndex>1</openSearch:startIndex>
<openSearch:itemsPerPage>25</openSearch:itemsPerPage>
<gCal:timezone value="America/Los_Angeles"/>
<gCal:timesCleaned value="0"/>
<entry>
<id>http://www.google.com/calendar/feeds/cqdcu7b550jienqk97ddrdfhpc%40group.calendar.google.com/public/basic/_6srj8chl6hhm4oppc9ij8oppcks3gp9n6kom6pb2cdij8c9gcpj3kc9d74ok6dpl8p246gpi6gqkae9j88s3gchl6t24cdhg60rk8di588s2qc9k68qjadpm6oo30c1g60mj2d1i6gs32e1i60pj0c1g</id>
<published>2015-02-24T23:02:37.000Z</published>
<updated>2015-02-24T23:02:37.000Z</updated>
<category scheme="http://schemas.google.com/g/2005#kind" term="http://schemas.google.com/g/2005#event"/>
<title type="html">Project Manager Meeting</title>
<summary type="html">When: Thu Mar 5, 2015 9:30am to 10:30am&nbsp;
PST<br>
<br>Where: Conference Room NH2/CA Motor City S Vermont 12345@KAIPERM
<br>Event Status: confirmed
<br>Event Description: Chairperson: Resource-Scheduler
Required: Test User 2</summary>
<content type="html">When: Thu Mar 5, 2015 9:30am to 10:30am
PST<br />
<br />Where: Conference Room NH2/CA Motor City S Vermont 12345@KAIPERM
<br />Event Status: confirmed
<br />Event Description: Chairperson: Resource-Scheduler
Required: Test User 2</content>
<link rel="alternate" type="text/html" href="https://www.google.com/calendar/event?eid=XzZzcmo4Y2hsNmhobTRvcHBjOWlqOG9wcGNrczNncDluNmtvbTZwYjJjZGlqOGM5Z2NwajNrYzlkNzRvazZkcGw4cDI0NmdwaTZncWthZTlqODhzM2djaGw2dDI0Y2RoZzYwcms4ZGk1ODhzMnFjOWs2OHFqYWRwbTZvbzMwYzFnNjBtajJkMWk2Z3MzMmUxaTYwcGowYzFnIGNxZGN1N2I1NTBqaWVucWs5N2RkcmRmaHBjQGc" title="alternate"/>
<link rel="self" type="application/atom+xml" href="https://www.google.com/calendar/feeds/cqdcu7b550jienqk97ddrdfhpc%40group.calendar.google.com/public/basic/_6srj8chl6hhm4oppc9ij8oppcks3gp9n6kom6pb2cdij8c9gcpj3kc9d74ok6dpl8p246gpi6gqkae9j88s3gchl6t24cdhg60rk8di588s2qc9k68qjadpm6oo30c1g60mj2d1i6gs32e1i60pj0c1g"/>
<author>
<name>SB Meetings</name>
<email>yy.yy@gmail.com</email>
</author>
</entry>
<entry>
<id>http://www.google.com/calendar/feeds/cqdcu7b550jienqk97ddrdfhpc%40group.calendar.google.com/public/basic/_c9ijacj668sj0or16dh38chmcos3eohk64smcdpm64qjce1k6kq3kc9d64qj0g9h65330dq16kojedq170s3gchl6t24cdhg60rk8di588oiqc9k68q36dhn60o30c1g60mj2d1i6gs32e1i60pj0c1g</id>
<published>2015-02-24T23:02:37.000Z</published>
<updated>2015-02-24T23:02:37.000Z</updated>
<category scheme="http://schemas.google.com/g/2005#kind" term="http://schemas.google.com/g/2005#event"/>
<title type="html">Analyst Meeting</title>
<summary type="html">When: Thu Feb 19, 2015 9:30am to 10:30am&nbsp;
PST<br>
<br>Where: Conference Room NH4/CA Motor City S Vermont 12345@KAIPERM
<br>Event Status: confirmed
<br>Event Description: Chairperson: Resource-Scheduler
Required: Test User 1</summary>
<content type="html">When: Thu Feb 19, 2015 9:30am to 10:30am
PST<br />
<br />Where: Conference Room NH4/CA Motor City S Vermont 12345@KAIPERM
<br />Event Status: confirmed
<br />Event Description: Chairperson: Resource-Scheduler
Required: Test User 1</content>
<link rel="alternate" type="text/html" href="https://www.google.com/calendar/event?eid=X2M5aWphY2o2NjhzajBvcjE2ZGgzOGNobWNvczNlb2hrNjRzbWNkcG02NHFqY2UxazZrcTNrYzlkNjRxajBnOWg2NTMzMGRxMTZrb2plZHExNzBzM2djaGw2dDI0Y2RoZzYwcms4ZGk1ODhvaXFjOWs2OHEzNmRobjYwbzMwYzFnNjBtajJkMWk2Z3MzMmUxaTYwcGowYzFnIGNxZGN1N2I1NTBqaWVucWs5N2RkcmRmaHBjQGc" title="alternate"/>
<link rel="self" type="application/atom+xml" href="https://www.google.com/calendar/feeds/cqdcu7b550jienqk97ddrdfhpc%40group.calendar.google.com/public/basic/_c9ijacj668sj0or16dh38chmcos3eohk64smcdpm64qjce1k6kq3kc9d64qj0g9h65330dq16kojedq170s3gchl6t24cdhg60rk8di588oiqc9k68q36dhn60o30c1g60mj2d1i6gs32e1i60pj0c1g"/>
<author>
<name>SB Meetings</name>
<email>yy.yy@gmail.com</email>
</author>
</entry>
</feed>
the result will be:
<?xml version="1.0" encoding="UTF-8"?>
<items>
<item>
<title>Project Manager Meeting</title>
<when>Thu Mar 5, 2015 9:30am to 10:30am
PST</when>
<where>Conference Room NH2/CA Motor City S Vermont 12345@KAIPERM
</where>
</item>
<item>
<title>Analyst Meeting</title>
<when>Thu Feb 19, 2015 9:30am to 10:30am
PST</when>
<where>Conference Room NH4/CA Motor City S Vermont 12345@KAIPERM
</where>
</item>
</items>
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