According to the documentation found at

Checking the Completion Status of a Task You Sent
In the Tasklist folder, you can check the status of any task you send.
NOTE: You can only check the completion status of tasks. You cannot check the status of e-mails and
other item types you sent to other people.
1 Open the Tasklist folder.
2 Open the task you want to check.
3 Click the Properties tab.

I sent a task to my coworker, he accepted it, but it does not show up in my tasklist folder, so it kinda fails at step 2. Is there something I need to do?