The NCIS team never goes anywhere without a knife! Collected here are a number of knives from different episodes.
Gibb's Knife, the ZT301. The blade that from the steak scene at the end of "Flesh and Blood". Also given critical appearances in "Enemies Foreign and Domestic" and "Obesssion".
Tony's knife that from the steak scene at the end of "Flesh and Blood". The black model of Gibb's knife.
Ziva saves Ducky using the Cold Steel Kobun as a throwing knife in "Silver War”. The knife returns in S4E5 “Deception” and S4E1 “Shalom” including the knife throwing training in S4E15 “Friends & Lovers”.