Hi Sachin,
I think that my past answer explained this poorly. The breadcrumb you mention (Admin > Email > Branding Domain) is what you do to find your branding domain in Marketo.
When you are in Google Analytics, you want to go to the analytics for your domain (Home > [your domain/website]), you then want to go to to Acquisition > All Referrels (on the left hand side). This shows you all the traffic on your website that has come through referrels. If you have enough traffic coming from Marketo you should see your branding url appear, if not you can search just above the table (below the graph) for your domain. I have hopefully included a good screenshot of this for you (our branding URL is i.thedrum.com):
I hope this helps.