Want to add a link below "Favourites" on listing page

Hello,
I would like to add a link below favourites for each listing (gd_place).
I am using CPT and custom fields. The link must have the format

http://site.url/page_name/?custom_field_key=custom_field_value&custom_field_key2=custom_field_value2&custom_field_key3=custom_field_value3#link

The Key(s) & values need to come from the listing’s custom fields & values.
I have read a number of your Docs and many forum postings and I can’t figure out how to do this.

Could you please direct me to the documentation for the the best way to do this?
Is it a hook / action in the functions.php? or a modified theme template file.

Thank you for your assistance.