Ok. I have a Jirachi with Wish and I use it. Then if my opponent uses HealBlock on Jirachi, would Wish take effect?
Heal Block prevents the functioning of the moves Ingrain, Aqua Ring, Moonlight, Morning Sun, Roost, Recover, Heal Order, Rest, Softboiled, Wish, Milk Drink, Slack Off, and Synthesis, while it is under effect. The player can still use items such as Potions to heal the Pokémon.
To sum it up it would take effect but you will gain nothing out of it.
Source
