How to know which forms accepting credit card payments?

Is there a way I can tell which forms (created by my sub-account users) accept credit card payments?

If the forms are created by the sub-account user in your account, you may check them directly from your account. If the forms are created in their accounts and not shared with you, unfortunately, it is not possible to know the details of the form. In this case, if you have the form URL you may clone it to see if any payment field is added to the form.

Hope this information helps! Let us know if you are referring something different. We will be happy to help. 

Since we have hundreds of forms, that would be a difficult task for me to open each form and search for a payment widget.  Is there any way of finding out how many forms have added a particular widget?

Unforutnately, it is not possible to check for a particular field/widget for different forms without opening them. It is required to check the forms manually and separately.