How do I register for a tournament that appears in the FIDE website but not on chess-results? Here is this tournament on the FIDE website. However, there are no contact details, no venue mentioned and the tournament does not appear in the chess-results database. How do I register for such a tournament?
FIDE used to publish contact details for arbiters but they no longer do so. However if you can look up any of the three mentioned arbiters and find contact details locally that would be your quickest route.

Failing that your next best bet would be to contact the Sudan Chess Federation. There the email address is given as sudanchessfed@yahoo.com and the phone number as +249916177000. Additional (different) phone numbers are given for the president and two vice presidents. You could also try these.