Tricky question, some are different but most of the time you will cross the chains forming a “X”, what this does, if your trailer was to come unhooked crossing the chains will help control the trailer from going one way or another, instead it’ll still follow you and theoretically allow you to pull over safe. 

How should a trailer's safety chains be attached to the towing vehicle?

Safety chains should be crossed under the trailer tongue and securely attached to the towing vehicle’s hitch or frame-mounted chain loops. Crossing the chains forms a cradle that helps catch the tongue if the trailer becomes disconnected, preventing it from dropping to the ground. The chains should be long enough to allow for turning, but not so long that they drag on the ground or get caught under the coupler or hitch.

Never attach safety chains to a bumper or any non-structural part of the vehicle. Always inspect chains for wear or damage, and use hooks with safety latches to prevent accidental unhooking during travel.