祖 is built from the 礻 (altar / spirit (left)) and 且 components.
It reads ソ like 且, as do 組, 阻, 粗, and 租 — learn 且 once and the family's reading comes with it.
A common word using 祖 is 祖父 (そふ), meaning “grandfather”.
Don't confuse it with 社, 神, and 祝.
