I wonder if jumping even makes sense at 6x gravity... maybe they would never have learned how to jump at all and always keep some limbs in contact with the ground.

Or if "humanoid" even makes sense. Something snake like that can spread out the pressure along a longer surface might be better. Or at least something with more than two legs.

What body shape would creatures living at six times the gravity even have? Would they be able to jump? Would they have a skeleton as we know it?

I would almost go looking at deep sea creatures that have to deal with extreme pressures on earth.

They might have to be entirely aquatic at that point or perhaps have some very exotic skeletal structure that can support their weight. Perhaps ball shaped beings who roll around instead of any sort of walking? I'm unsure how would they deal with a small incline.

Weight lifters are able to lift 6x their body weights, but it's not a sort of load that we could profitably exist under long term. We'd need to have extremely thick limbs and at some point that won't help either because of the cross-section vs. weight scaling law. It's also a sort of weight where any kind of leverage against a joint will generate massive forces. E.g. try catching a 50kg falling weight, you are likely to dislocate your joints and/or break some bones. And yet 1/6 of that is entirely manageable.