Hi Jignesh,
Partner ID is the subdomain assigned to your Organization, you can check with your Adobe Consultant or Account manager to know the AAM subdomain of your account.
You will also see that subdomain in Visitor ID calls like this : <subdomain>.demdex.net (apart from dpm.demdex.net)
While implementing AAM, you just need to put the partner id in double quotes.
Thanks,
Varun Kalra