just the head shake

How do you want it to appear visually? Eg in real world you would see more hair as head leaned forward etc. Do you just want head to move up and down, or different artwork?

If different artwork, you can draw head leaning forwards then use triggers and a swapset to replace the default head. Basically you draw the head in the other position.

The head and body are all connected (no independence at present) so head moves will move body as well if you just use a dragger. There are things you can try for up/down like putting a Transform behavior on the Head layer then record with keyframes the YPosition going down and up. You can then turn this into a replay if you like, so you can trigger it.

Another approach if a once off is to put dragger on head and neck. Drag and record the neck/top of shoulders one pixel (that will lock it in place) then drag head down and up. See what it looks like.

The other thing you can try is making the head independent - again using transform behavior above to move it. Head movements then will never affect the body. There are other side effects though - try it and see.

So a few things to experiment with - you need to decide which looks visually consistent with the rest of what you are doing.