You can start this contract by talking to Derek in his base camp over the Imperial Testing Station 2.

You need to be Rank 3 with Atreides to be able to talk to Thufir Hawat. If you weren't Rank 3 at the time you accepted to quest, you might have to cancel it and re-take it again from Derek.

If you are Harkonnen, please see https://dune.gaming.tools/contracts/ct_trainer_planetologist2_04_hark instead.