So… There are rumors of a sandworm in the Chapterhouse desert. As of now the desert has only produced small sandtrout. Go talk to Sheeana the Bene Gesserit Reverend Mother.
Sheeana resides in the big complex in the southern desert of chapterhouse. You must offer to aid her.
She wants the mother superior to accept you. For this you must find mother superior Odrade and ask her to 'test' you. Odrade lives in the northern part of Chapterhouse. To pass the test you must observe everything the room she sends you to and then answer correctly five questions about the room. A failure is punished buy her bodyguards. Hint: If you fail the test and survive the bodyguards, you can try 'test' to answer again or you can 'cancel' the test and then try the test again with a new chance to observe the room.
After passing the test you must return to Sheeana and 'confirm' that Odrade accepted you. She will give you a voucher to purchase a thumper or a recording device.
Thumper can be purchased near the Chapterhouse AP. The seller will also give you a hint where the sandworm is to be found.
The recording device can be found in the southwestern outpost of the desert. The equipment room requires high-level identification. There's a high-ranking reverend mother in the no-ship, whose identification you might “borrow”…
Now just go find the worm…