I converted trad IRAs to Roth IRAs in prior years. I'm trying to report them in TurboTax now. TurboTax is asking if they're taxable or nontaxable, I'm not sure.

If you had no basis in nondeductible traditional IRA contributions and did no rollovers to an IRA of after-tax money from a qualified retirement plan like a 401(k), all of your Roth conversions were taxable conversions.  If any part of a particular conversion was from basis in nondeductible traditional IRA contributions or from after-tax money in a qualified retirement plan, that part would be a nontaxable conversion.

They are taxable when you convert them. Roth IRAs are not taxable when you withdrawal them.