？
Do you get what I'm trying to say?
Literal
I [of-の] want-to-say thing understand?
言いたいこと ('things [I] want to say') combines ~たい (desire) + こと (nominalizer) + the possessive 僕の. The absence of a subject/particle on わかる is typical casual — 'understood?' The full polite would be わかりますか.