Depends on what you mean. If you have already evaluated Python code, such as "x = 42" then you can get access to the value bound to x in Javascript like:
Sk.globals["x"].v
If you want to make a Python value in Javascript and put it in the Python environment, you could:
Sk.globals["new_x"] = new Sk.builtin.nmber(125);
(I've only been working with Skulpt for a short while, so take this advice with a grain of salt.)
Hope that helps,
-Doug