The translation being shown to me is 'is it frequent', but I'm wondering then why the 'αυτό' is required? Surely for this you would just say είναι συχνό;
Is it correct to say that the following is a more exact translation;
Είναι συχνό; - Is it frequent?
Είναι αυτό συχνό; - Is this frequent?
No; as far as I know, συζήτηση is from συν- + ζητ- + -ηση and θέση is from θε- + -ση.
The -ηση and -ση are the same, though, I believe; an ending turning a verb into a noun describing that action (an action of requesting-together or an action of putting, respectively, from ζητώ "request" or θέτω "put").
θέτω was originally a lot more irregular, coming from Ancient Greek τίθημι which had a stem of θε- and no thematic vowel.