All you need to do it select your mesh and go to "Geometry > Freeze..." in the top menu bar. Make sure 'Freeze Deformation' is selected and press OK. It should now be posed and ready for sculpting.
Also, for future reference, to see stuff like this in the modeling viewport hit 'O' and turn on "Enable Deformers". That will show the mesh in it's deformed, AKA posed, state.
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But to export, yes, you'll need to freeze geo.