The email template is in SD.EmailServices and you'd be looking for [Model 9] Incedent.Satisfaction Survey. The URL is in Satisfaction Survey Body. You can either change the variable to the exact location of the URL (not the preferred method) or change the Profile Property for the link.
By default the link should be the variable:
[ProfileProperties].service_desk_settings_customer_service_survey_url
which is accurate
The profile properties should be pulling in from the ServiceDesk Profile inside of Process Manager which should really just be your server name. The complete URL is this
https://servername/sd.customerservicesurvey/Composer.aspx
You may not be using https and servername should be the name of your servicedesk server.
Go to Admin - Data - Application Properties.
Click on ServiceDeskSettings and scroll down to Category:Services
You'll probably notice that the URL isn't fully pathed out to include the servername.
Edit the page and append CustomerServiceSurveyURL to include the full path and then save it.
Do an IIS restart and see how it goes from there.