Yes, thank you Wendy, I forgot the comma...

Hello Beatrice, you just need a comma after 'right', (as you had in your first translation) and I would also leave out the second 'on', sounding more natural in spoken English :))
Is he going to sit on the left or the right, your centrist?

Oh bien sûr, merci !

Is he going to sit on the left or on the right, your centrist?

Hello Beatrice, in English it is unusual to form a question in this way. We almost always inversion.
Is he going to sit on the left or the right, your centrist?