"I ask him to speak slowly."
Translation:Jag ber honom tala långsamt.
It's not about politeness, but be means ask as in 'ask someone to do something', whereas fråga means 'ask' as in 'ask someone a question'.
I'm guessing you're on mobile, since there's a known problem with discussions not showing up properly for mobile users. Hopefully Duolingo will fix this eventually.