Depends on what truck and tires you have and payload. You can follow the manufacture's recommendation on the door sticker. You can also weigh your truck and inflate them to a safe margin above the minimum for the loaded truck weight. In my case, my stock General Tire Radial Grabber HTS LT245/75R-17E tires are inflated to 65 psi in the front and 80 psi (max cold tire pressure) when towing my fifth wheel trailer due to the added payload.
2022 Jayco Pinnacle 36SSWS / 2016 Ford F350 6.7L Diesel Crew Cab LB DRW 4x2
2022 Thor Palazzo 33.6 diesel pusher / 2021 Chevy Equinox LT AWD toad