Which compound (Samas) is present in the word 'पंकज' (Pankaj)?

'पंकज' means 'पंक (कीचड़) में जन्म लेने वाला' (born in mud). Instead of pointing to mud or birth, it points specifically to a third unique meaning, which is the Lotus flower ('कमल'). Hence, it is a Bahuvrihi Samas.