The ornamental design for a round-ended cook's knife, as shown and described.
FIG. 1 is a front-side perspective view of a round-ended cook's knife showing my new design.
FIG. 2 is a rear elevational view thereof.
FIG. 3 is a right side elevational view thereof.
FIG. 4 is a front elevational view thereof.
FIG. 5 is a left side elevational view thereof.
FIG. 6 is a bottom plan view thereof; and,
FIG. 7 is a top plan view thereof.
Stippling and shading lines shown in the drawings are intended to represent the approximate three-dimensional contour of the design, and are not intended to indicate surface decoration. Features depicted in broken lines form no part of the claimed design.