Unfortunately, apart from laying it out on a chassis table, it’s tough to tell unless it is really badly bent.

You could get an idea with a tape measure and a level.  Do your transverse corner measurements (front left, right rear, front right, left rear).  They should be the same.  Then set the chassis up on three jack stands, two on the rear, one center in the front.  Put a 3′ level across the top of the rear bearing hangers and level the chassis.  Then swap the level to across the front axle brackets.  Should also be level.

That being said, it’s common for a chassis to have a twist to it right from the factory, they are easily twisted back.

CR

Would Sniper alignment tool be helpful?