IUPAC name of C₆(CH₃)₆²⁺
From the IUPAC Gold Book:


  Carbocations may be named by adding the word 'cation' to the name of the corresponding radical. Such names do not imply structure (e.g. whether three-coordinated or five-coordinated carbon atoms are present).


So since this is the dication of hexamethylbenzene, it would probably  least incorrectly be called hexamethylbenzene dication. At the very least, this seems to be how a lot of people refer to it (or more verbosely, pentagonal-pyramidal hexamethylbenzene dication).