Is it normal for ejaculation to hurt on my scar where they removed my testicle?

Painful ejaculation. It's probably normal to experience pain for a while after your testicle is removed when you ejaculate because the testicles draw up into the scrotum just before release. Altho the testicle is gone, the muscles that cause that are still there and they can pull against scar tissue causing discomfort. As scars soften, this will lessen but if it's too severe or more than a year, see your doctor.
No. The divided end of your spermatic cord or the divided cremaster muscle may have be adherent to the scrotum by scar and might contract during ejaculation/orgasm.