I'm trying to add a detail link to an HTML Email template, to link to a related record on the object being merged into the e-mail.
I am aware of the process for adding a link/detail link for the object in the template by using
{!Communication__c.Link}
But my Communication object has a lookup to a Case called ParentId__c (which I can be sure is not null..) and I want to link to THIS object... my initial thought was to use
{!Communication__c.ParentId__r.Link}
and it would traverse the relationship, and then merge out the Link value as with other objects, but this has not worked.

Hello,

This is my apex email body in the code.

   String body = 'Dear ' + con.firstname + ' ' + con.lastname + ',   ';
body += 'Thank you for considering us for your on-going software development needs. We sincerely value the opinion of our customers, and we would love to hear your opinion on our services which would help us improve the same.Please take a few minutes to complete the Feedback form by visiting the link given below.' ;
body +=  'Here’s the link  https://appfeedback-developer-edition.na30.force.com/survey/?email='+con.email+'&fullname='+con.firstname+ +con.lastname
 body += 'Best Regards,' ;

I want each of these lines on the new line.Currently it is displaying  in email as.

Dear Tejas Wadke, Thank you for considering us for your on-going software development needs. We sincerely value the opinion of our customers, and we would love to hear your opinion on our services which would help us improve the same.Please take a few minutes to complete the Feedback form by visiting the link given below. Here’s the link https://appfeedback-developer-edition.na30.force.com/survey/?email=tejas.wadke@aress.com&fullname=TejasWadkeBest Regards,https://www.tester.com?fullname=con.firstname+con.lastname