As per title, what is the name of a group of dragonflies? Some friends say it is a mob, some say it is a hover. Anyone?
A large or dense group of flying insects is called a swarm.
You could also say a bunch of dragonflies.
The Ngram of "a * of dragonflies" shows only three results: swarm, pair and couple.
I've also looked at how swarm compares to other suggestions so far (e.g., flight, cluster, beauty, cloud, bunch, glimmer, squadron, mob, hover) in another Ngram, which shows that Ngrams are not found for any of the other suggestions.
Therefore, I think you should go with swarm.