Did dinosaurs have a tongue and if they did, do we have an idea how far it goes back?

Dinosaurs currently have a tongue. Birds are dinosaurs, and birds have tongues. As mammals and birds share a mouth and tongue - as do many species of "fish". It's likely that that structure predates mammals and birds (and therefore dinosaurs)

Most non-avian dinosaurs, then, probably had relatively simple, flat tongues like those in the mouths of today’s alligators and crocodiles. The shovel-beaked hadrosaurs and the armored ankylosaurs may have had more elaborate tongues - the better to help them cram plants into their mouths - and early birds began to get more elaborate tongue apparatus, but it seems most non-avian dinosaurs would have been incapable of giving you a Bronx cheer.

This short article is actually fascinating, it’s all about dinosaur tongues:

https://blogs.scientificamerican.com/laelaps/what-did-dinosaur-tongues-look-like/

usually to the back of the throat and yes