The relative path is the path from the repeating node. Your repeating node is: my:expenseReport/my:items/my:item
Your relative path would be:
<my:Mapping>
<my:FormField my:IsRichText="false">../../my:employee/my:name</my:FormField>
<my:SharePointColumn>User</my:SharePointColumn>
</my:Mapping>
<my:Mapping>
<my:FormField my:IsRichText="false">../../my:employee/my:emailAddress</my:FormField>
<my:SharePointColumn>email</my:SharePointColumn>
</my:Mapping>
I'm assuming that this has the full path because that is what you entered in the mapping tool. One way to figure out the relative path is to set up a rule on your repeating group. Add a condition. For the first drop down for your condition, select the field you want (like name in the above example). Then change the first drop down to "The expression" - you'll see the relative path in the text box that displays in the condition. Then you can delete your rule.