Learn Spanish (Latin America): ¿Qué estará jalando ahora ese mimo?

This is the future progressive used for present conjecture. By combining the future of estar with a gerund like jalando, you express a guess, doubt, or wondering about an action happening right at this moment. It is the Spanish way of saying "I wonder what he is pulling" or "What could he be pulling?"

I previously learned tirar for "to pull". Is jalar common?

Yes, in Latin America, jalar is the most common, everyday verb for pulling a physical object. For example, if you look at doors in Mexico or Colombia, the sign for "Pull" will almost always say Jale instead of Tire.

Could I just ask "¿Qué está jalando ahora ese mimo?" instead?

You could, but it changes the meaning. Using the present progressive (está jalando) makes it a direct request for factual information: "What is that mime pulling now?" Using the future progressive (estará jalando) turns it into a speculative guess: "What on earth could he be pulling?"

Why is the subject ese mimo placed at the very end of the question?