Hey Tomas,
It is typically recommened to use the Environment Library for these placeholder type fields so you can manage their values across different environments like Development vs Test vs Production. Take a moment to review this topic at help.k2.com: Understanding Environment Libraries. We also have a more indepth whitepaper if you have more time to review: K2 Environment Library WhitePaper. There's a PDF you can download there.
If you're on K2 4.7 or K2 Five, you can reference the Environment Fields from the fields tab in in the Context Browser as shown below. Keep in mind though, when sending a task assignment notification to one of your users, K2 will automatically include a link to your form for that task in the task notification message, so you don't necessarily need to include a link there manually unless you want to provide a link to another URL that servers a purpose for the assigned task.
Hopefully this helps you get going in the direction you need. Write back if you have more questions. If you haven't gone through any training or tutorials yet, you might try reviewing the Hello World tutorial here, which will get you going with some of the basics in working with forms and workflow. You should be able to get an idea of where things are and how to move around some of the editing environments.
Regards,
Jason
Thanks!! I finally figured it out yesterday afternoon. (Seems so simple when you know where to look! haha).
-tomas
Great! Glad to hear you solved it!
:)