Do they have combat experience: YES
Do they have magical skills: YES
Current abilities:

Hydrokinesis: Ability to manipulate and create water through his vision, including ( but not limited to) transforming water into solid objects like weapons that maintain the quality and deadliness of its physical steel counterpart. He is also technically capable of a lot of other things that are less considered. If it has water in it, he can manipulate it or otherwise do things to it that are not often considered.

He can't actually teach this to anyone, however, as it's done through his vision.
Master of Weapons: He can train anyone in any weapon they desire, but his weakest skill is with the bow.

Childe will just smile and shrug if asked about any further abilities once he lists those two.
Abilities of OTHER characters mine would reveal: NO.
I want to participate in Training Logs/Activities: YES
Training Activities Suggestions: He won't give any, and you don't want his suggestions, anyway. He comes from fake!Mother Russia, and it's been shown and referenced that they do less than humane things for the sake of making super soldiers as strong as possible.
When should the first Training Log occur? whenever's good for the majority.