It depends on the age. If they are under 13, the account would need to be created in a parent or legal guardian’s name. If they are 13+, the account can be in their name with Parental Controls set up.
If he plays Overwatch 2 on console he definitely has a Battle.net account, since it is required to link the two. You should see his BattleTag in your friends list, unless you have him as a RealID friend.
If you right click on his profile in your Battle.net Desktop App it will show you his full BattleTag. You’d have to ask him what email he is using if you want that.
To start a World of Warcraft account you really only need game time. So you can buy and gift him game time through the shop or you could help set up a subscription for him.
A subscription just grants the base game, up through the Shadowlands expansion. You can gift him Dragonflight or pre-purchase the next expansion The War Within (which includes Dragonflight).
If he has characters on your account and you want to allow him to keep playing them, you’ll need to use the Character Transfer service. You should be able to gift him Character Transfer Tokens through the shop (they are currently on sale right now).
He’ll need one for each character he wants to transfer, so depending on how many that is, it might get expensive.
Assuming you share the same last name, and that is what he used to set up his Battle.net account, transferring characters from your WoW license to his should be easy enough. As Vorsol noted though, any Battle.net account bound item like mounts, heirlooms, appearances, toys, etc… will not transfer with the character so they will have to earn their own collection on their account.
If the names do not match, we may still be able to help but you’ll need to submit a Support ticket.
Hopefully that covered everything, but let us know if you have any other questions.