How many skills does it need?
SELECT   count ( * )  FROM Parts AS T1 JOIN Part_Faults AS T2 ON T1.part_id   =   T2.part_id JOIN Skills_Required_To_Fix AS T3 ON T2.part_fault_id   =   T3.part_fault_id   GROUP BY T1.part_id ORDER BY count ( * )  DESC LIMIT 1
count number of skills needed for the part with the most faults; involves joining Parts, Part_Faults, and Skills_Required_To_Fix tables;