Exhausing a Card

In a fight I used the Hard Knocks card, paying 2 resources.

Do this exhaust the card, or can I use it in another attack in another action in the same round?

Hard Knocks do not have an action trigger but a free trigger.

Edit: your topic title and question don't seem to agree. I've answered the question as written, but if it is incorrect you can edit it with the "Edit" button at the bottom-left of your post and I'll update my answer.

Cards don't exhaust unless they explicitly say that they do - exhausting is an extra cost that is required by some cards.

For Hard Knocks, you pay 2 resources to play the card and put it into your play area. After that, during any combat or agility skill test, before drawing a chaos token you may spend any number of resources and get +1 for each resource spent.

Because the only cost of Hard Knocks is resources, you may use it on any skill test at any time as long as you have the resources to do so. It is not limited to one skill test per round.

Hope that helps.