The Hogwarts professors would have mixed reactions. Dumbledore would be very diplomatic and open - minded. He would try to establish communication and see how the Yautja King could fit into the grand scheme of things in the wizarding world. Snape might be more suspicious and view the Yautja King as a potential threat to the safety and secrecy of the wizarding world. But as the Yautja King proves himself, Snape's opinion might change. And the students would be mostly in awe and a bit scared at first, but then some of them would be eager to interact with this strange and powerful being.
Well, the Ministry of Magic would likely be in an uproar. They are used to dealing with magical threats and the Yautja King, being an alien, would be completely out of their realm of understanding. They might try to capture or contain him at first. But the Order of the Phoenix might see the potential in having the Yautja King as an ally. Harry and his friends would have to convince the more stubborn members of the wizarding community that the Yautja King is not a foe. And characters like Hagrid would probably be one of the first to approach the Yautja King in a friendly manner, being more open to new and strange creatures than most.