How to lock to penis, add bones, parents item?
There are TWO WAYS to parent objects in KK studio. The most intuitive way is workspace parenting and this is how you would handle simple object parenting. For reference, parenting means the child object inherits the same motion properties of the parent. This means the child would move the exact same way as the parent, just by some particular offset (like wherever you position the child).
So lets say you wanted to add a nipple piercing to a character. You would expand that character's tree in the workspace, then expand "torso". This would show you further nodes like L. Nipple, R. Nipple, Mid Back, etc. To parent the piercing to one of those nipples, you'd just click the name of the nipple you want, hold CONTROL and then click the piercing to select both of them. Then you'd click the "parent" button at the bottom of the workspace.
This will move the object underneath that particular node of the character within the workspace, and the object will now inherit the same motion of the nipple you've parented it to. You can still adjust the position, rotation, and scale of an object which has been parented in the workspace. So if it's not lined up right, you can just further tweak the position using the translation controls. This is what you'd do with a penis, or bone collider, or whatever.
Workspace parenting follows very specific rules: the FIRST thing you click will become the parent, the SECOND thing you click will become the child of that parent. This is how you can organize a scene into folders as well! It's just parenting folders together to create an organized workspace. But if parenting doesn't seem to have the results you thought you'd get, or if it just didn't do anything whatsoever, you may have the order of things you've clicked on backwards. To remove a child from a parented object, just click it in the workspace and click "release." This will kick it to the bottom of the worskpace.
The second form of parenting involves the use of NodeConstraints. This is still not very complicated but it is much more involved. It's basically no different than parenting stuff in the workspace, the difference is NodeConstraints allows you to functionally use any combination of bones on the character to serve as parents or children. This is how you can get a character's hand to stay attached to part of another character's body, while the rest of their motion stays intact. Or how to make a bed move using position motion from, say cf_j_spine_01 or whatever. NodeConstraints is just less intuitive to work with, but it provides much more granular control.
I think those interested in this, we need a video guide on this. I don't know how you learned, but if you find something like this, please, we would be very grateful if you share it here, I would like to know how to move the buttocks of the girls manually. I understand that it is similar to what you explain, but beyond that, I have no idea how to do it. Lol
I've learned most of this by extensively dissecting existing scenes to figure out how they work, as very rarely is it possible to just swap a character or change one singular thing. Most of the time these animations break quite extensively when doing this, so they must be tweaked or altered to make them look as good as the original. I've never made my own animations, but I've extensively modified tons of them, sometimes changing big parts of how the animations work, even spliced them together to create longer animations and such. I may work on a simple video to demonstrate how to do some easy things. Really, knowing how to parent in both workspace and adjust existing nodeconstraints and how to use bone colliders can get you pretty far.