tools -> decompile hl-> decompile hl models and then select a mdl file (example goku.mdl)
decompile it and then go File-> import-> halflife smd and select the goku.smd, it should open a model of goku , and if you dont see the skeleton, then go to the right bar and select skeleton/joints -> show skeleton
i dont really remember the names of the tool bars but they should sound similar to that.