OIM - Fetching OIM UDF data in SOA composite

<assign>
    <copy>
        <from variable="getApproverDetails_OutputVariable"
                   part="UserData"
                   query="/ns20:UserData/ns20:CustomAttribute[@Name='YOUR_UDF']/ns18:Value"/>
        <to variable="YOUR_VAR"/>
    </copy>
</assign>

Example:

<assign>
    <copy>
        <from variable="getApproverDetails_OutputVariable"
                   part="UserData"
                   query="/ns20:UserData/ns20:CustomAttribute[@Name='Email']/ns18:Value"/>
        <to variable="approverEmailID"/>
    </copy>
</assign>