Can I tell my dad to put a shirt on?
Why do you want him to put on a shirt?
It makes me feel awkward when he doesn't have a shirt on.
I get being uncomfortable around your dad if he's shirtless, but you really shouldn't tell your dad how to dress. He's allowed to go shirtless in his home if he wants to. It's pretty rude to ask someone to put on more clothes.
It's good for him to hear he should put on a shirt once in a while.
He's pretty much free to do what he wants in his own house. It's not like he's parading around completely nude. You should just ignore it.