Bipod manufacturers could stand to be more clear about which mounting system they use!
The most common seems to be stud attachment, using the same stud meant for attaching a strap. That's actually a decent solid way of mounting and if you've got a stud already, and a Harris or similar that wants to mount to it, you're already set to go shooting with it. Granted, it takes a minute or two to attach or remove.
Other systems include Picatinny rail, M-Lok, or Arca/RRS. The latter would be the premium system, making it easy to mount/unmount/adjust quickly and leaving a smooth underside for when you don't want the rifle catching on other things you're using as a shooting base.
I wouldn't go out of my way to add an underside Pic rail if it didn't have one already. It and M-Lok can actually make it harder to mount or dismount your bipod and oblige you to find appropriate tools unless you have one designed for tool-less mounting.