How is "Chult" pronounced? Is it /tʃʌlt/ or /tʃʊlt/ in IPA?
Chult, as pronounced by Wizards of the Coast employees, rhymes with cult. I believe the IPA would be [tʃʌlt]. You can hear WotC employees talk about Chult on almost every Dragon Talk podcast from March 30, 2017 through today anywhere you find podcasts or on the D&D website. This one has a segment about Chult starting at 7 minutes in.
Chris Perkins from Wizards of the Coast pronounces the name of Chult in the video "Tomb of Annihilation: Chris Perkins Talks Story, Death and Collaboration" (around 1:34 into the video).
He pronounces it [tʃʌlt].