Question: I was wondering about one thing. In my sentence, would it be “he’d had enough” or “he had enough”?
He’d had enough. He could handle his sister’s complaining, but…
Answer: “He’d had enough” will work better for you.
“He had enough” is usually quantifiable, eg: “He had enough breakfast cereal to last for a year”, means he’s got enough cereal stocked up in the pantry to last that long.
Whereas “He’d had enough breakfast cereal to last for a year” means he’s so sick of breakfast cereal he doesn’t want to have any more for a year.
So in this case, by using “He’d had enough”, you’re saying he’s sick of his sister’s complaining, and inferring that he doesn’t want to hear it any more.