牢 is a Chinese hanzi, listed here under the keyword “prison”. It is built from 宀 (roof) and 牛 (cow). It appears as a component in 2 other characters in this index.
On KumiJi Glyph Explorer, open the parts search and type “roof” + “cow”. 牢 is among the results, together with every other character containing the same shapes.
Open 牢 in the interactive kanji search
to expand every part down to its smallest pieces, add your own names and mnemonic stories,
or search for other characters by their parts.