Voightlander CL

I have a new/old CL, and manual says I can rewind film back into canaster...I'm think to do some double exposures, but not really sure of exposure setting w double images on same frame, any advice, I don't want to over expose, not sure of the correct technique?

It all depends on the subjects and which you want to be the strong and which to be the weak.
Total exposure should not be more than either properly exposed. Exposure 1 + Exposure 2 = The Total Exposure.
You'll undoubtedly have to experiment.

What film are you using. Something like Tri-X will give you a lot of flexibility.

I have been using B&W agfa APX, pretty cheap here in Köln...so total exposure should be about half for each frame, I thought as much

Seems intuitive, but no experience w this, all a big experiment, but that's what exciting shooting film

My only experience with this comes from:
1) accidental double exposures; or
2) the sort of cheesy things we used to do with wedding photos - think bride and groom in a wine glass.
For the latter, it was important to compose both photos with the other photo in mind. You want lighter details in one image to be juxtaposed with shadowed areas in the other. Otherwise they tend to block each other out. As the individual important areas didn't overlap, they would tend to need full exposure, or something close to it (like 1/3 of a stop less).
If you cut each exposure in half, only those areas where both images offer mid-tones will end up receiving the right exposure. Where shadows coincide, the result will be seriously under-exposed. The same may be the case for the highlights as well.
This sort of thing calls out for careful pre-visualization (as Minor White would have said).