I love both giving and receiving oral. My husband is one of very few lucky men that is married to a woman who actually enjoys giving him oral sex!
But he very rarely returns the favor

I don't know if he doesn't like doing it, if he is unsure of what or how he is doing or what. I will tell him that I will give him oral and he can return the favor and he agrees, but then never follows through.
How can I ask for this in a subtle way?