In the Forum thread, tap and hold the comment that you want to share.

There will be options available depending on the user:

As an admin, the available options are:
+ Reply
+ Share
+ Copy
+ Edit
+ Remove
+ Report

As a member, the available options are:
+ Reply
+ Share
+ Copy
+ Report

Simply tap on the Share button.

Once tapped, the available sharing app on your device will appear. There will be also a copy button that will allow you to copy the URL and paste it to i.e Comment or Message.

When someone clicks on the shared link and he is currently logged in to the members area on his device, he will be redirected to the comment page. If not, it will redirect him to the login page first and once logged in, he will be redirected to the comment page.