What is the adjective for something which has vertices?
You could try 'eight-cornered'.
Pointed
Usually you would say <number>-pointed with a hyphen, as in Eight-Pointed rather than Eight Pointed.
I wasn't able to find this usage in the dictionary pages for "pointed" itself, but plenty of adjacent concepts mention it, for example...
- (occult) A seven-pointed star with the construction lines retained.
https://en.wiktionary.org/wiki/heptangle
- A blue six-pointed star...
https://en.wiktionary.org/wiki/Star_of_Life#Proper_noun