The ornamental design for kitchen knife, as shown and described.
1.-2. Kitchen knife
1.1 : Perspective
1.2 : Front
1.3 : Bottom
1.4 : Enlarged right view
1.5 : Partial enlarged bottom view
1.6 : Partial enlarged bottom view
1.7 : Enlarged cross-sectional view
1.8 : Back
1.9 : Top
2.1 : Perspective
2.2 : Front
2.3 : Bottom
2.4 : Back
2.5 : Partial enlarged bottom view
2.6 : Partial enlarged bottom view
2.7 : Enlarged cross-sectional view
2.8 : Right
2.9 : Top
The broken lines in the drawings form no part of the claimed designs; the dash-dotted lines in the drawings represent the unclaimed boundaries; drawing nos. 1.7 and 2.7 are vertical cross-sectional views taken along an almost central plane of the blade in each front view.