The ornamental design for the kneeler base, as shown and described.
FIG. 1 is a top perspective view of the kneeler base showing my new and ornamental design;
FIG. 2 is top plan view thereof;
FIG. 3 is a rear elevational view thereof;
FIG. 4 is a front elevational view thereof;
FIG. 5 is a left side elevational view thereof;
FIG. 6 is a right side elevational view thereof;
FIG. 7 is a bottom plan view thereof; and,
FIG. 8 is a bottom perspective view thereof.
The broken line showing of portions of the kneeler base in FIGS. 7 and 8 is included for the purpose of illustrating environmental structure and forms no part of the claimed design.