How to change custom Ask button link to detect category?

Question

Hello

It was great that if you enter to a category and hit ASK Button its url change to ...?cat=2 or any number related to category that visitor hit ask button inside it.

Now I removed NAV and replaced by my custom image buttons. But inside each category url of button still is href="/ask" . How can I make it work just like Default ASK button?

 

Thanks alot