Nexus Clash

It is a 2AP action that consumes a nontrivial resource - I could see it give at least 5 XP, like blessing someone does
The AP/XP ratio would still be slightly worse than engineering (which can be done without any resource at all), so 5XP this would be a safe lower bound for a fitting value.

I'd generally consider 1AP/1XP to be the reasonable lower bound, especially since this is the rate of XP gained from a skill like Infuse. The only time you get worse is if you are intentionally doing something that you know is a bad AP/XP ratio (Lockpicking) or if you are crafting useful items for the future, such as potion-making.

That's not to say that 5XP for Anoint isn't worth it. After all, it does involve making or finding a potion to use for those XP, so it isn't exactly "free" to use and is worth giving it a bit better XP rate.