This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
玿 combines 王 (jade) with 召, which likely contributes the sound. The exact historical development is uncertain.
The left side is 王 (jade), and the right side is 召 (summon). Picture a rare jade artifact being summoned, but its true meaning remains hidden.
For ショウ, imagine a show where a mysterious jade piece is revealed: show -> ショウ, and the jade is the star of the show.