The people that you are renting the trailer from will tell you how much they want you to insure it for. That's probably written in the paperwork agreement also.
Then you call your insurance company and see what it will cost.
If you normally pull a different type of trailer you need to check with your insurance company and see if your rate will change and be completely transparent with them about what you are doing.
I'm assuming you have your own authority. If you do then you need also to update FMCSA if you are hauling a different commodity than what you have on file with them.
the person it's renting it's currently working under my company , no agreement at the moment , and i haven't find an agreement with insurance option yet, just hauling regular construction material