This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 皍 is uncertain. It visually contains 白 and 卩, but the original component relationships are unclear.
Since the meaning is unclear, focus on the shape: 白 (white) above 卩 (a seal or kneeling person). Imagine a white seal stamp, but remember the meaning is uncertain.
For ソク, imagine a sock (ソク) with a white top and a seal-like pattern on the bottom, matching the 白-over-卩 shape.