To many variables to access the repair with that picture. How about one a little further a way to tell where it is at? Also, what quality of a repair do you want?
Here is what I would do. First of all, any where there is a crack even in the gelcoat it needs to be repaired if you want it like new. Rigidity of the structure needs to be determined. If there is access to the back I would grind the back with a coarse DA disc and lay a new supporting layer of mat or cloth with resin, again, depending on strength needed.
Then I would grind out all damaged areas on the front side feather edging out to good material. Depending on the damage I would lay some mat and resin to build up the base and and add strength. If more build is needed I would fill with long or short strand fiberglass filler (kitty hair) keeping the surface a bit lower than the expected finish height. A skim coat of body filler blocked out to provide the finished base. A couple of layers each sanded if I want perfection. Urethane primer, sand, maybe prime again. Then either paint the whole panel or blend using a single or two stage catalyzed paint depending on the quality of the existing paint. Maybe color sand and buff, all depends. Either way, I could shave in the reflection of the paint
Maybe more than you planned on doing. It all depends on what quality repair you want. If I was to get carried away I would even spray a coat of new gelcoat.
For a cheap repair, grind it out, plaster it with kitty hair, sand, and paint it to your satisfaction. If you go that route, please don't ask me, "How's it look? I did it myself."
Good luck with the project and have fun if you do it yourself!