What's Meruem's nen type? So far in anime, I haven't seen any technique that shows what's his nen type.
I read the chimera arc years ago so I'm not sure, but I "think" I remember in a moment Meruem growing a pair of wings. If my memory is right, I'm not sure if that could be a natural ability or something related with an enhancement nen skill.
Is there any technique that gives some hints about his nen type?
According to the story, Meruem's initial ability gives him strength through consumption. His aura grows every time he devours a user of Nen, with their aura synthesizing to his own. This ability (Aura Synthesis) doesn't belong to any of the 5 basic categories, thus falls in the 6th category, making him a specialist. After absorbing large parts of Shaiapouf and Menthuthuyoupi, he was able to use their abilities too, making them his own. Further details about his new abilities can be found here.