I’ve never used Just Sketch Me but you can download posable figures and import into nomad. However, unless they’re already broken into a hierarchy, you’ll have to do it yourself. I’m guessing that’s why you may be having difficulty with your models from Just Sketch Me.
There are multiple models for nomad for free which are ready to be posed. Take a look at THIS post and you can get some models.
Also, look up @Holger_Schoenischka on the forums here as well as his YouTube channel: @ProcreateFX
He has some really in depth tutorials and I’ve seen him cover posing and mask extracting. He’s a great resource.