To track a task in which you are not the performer or the author, it is enough to find it and subscribe to updates.
How do I subscribe to task updates?
How to unsubscribe from task updates?
If you are not interested in the card, then you can stop following it:
What else do you need to know?
If you are mentioned in the card chat via @, then you will automatically follow the card
If you do not want to receive notifications on the card, but want the card to be in quick access, then add the card to Favorites