If I use Dragonair's "Dragon's Wish" attack and then on the following turn evolve it to Dragonite, can I still attach the energies or not?
Yes, absolutely! The Dragon's Wish effect resides on the player, not on the Pokemon.
Source: Sun & Moon FAQ (2017-02-02), TPCi Rules Team (2017-02-02)

Relevant cards

Note: All applicable cards may not be listed below.
SM1_95