睪 (gāo) is the Taiwan/traditional spelling for
睾 (gāo, 'testicle'). On the mainland the lower variant
睾 is standard, so
睪丸 vs.
睾丸 is the same word in different scripts. Don't confuse with the very rare archaic reading
睪 (yì), 'to spy out from a height', found only in classical texts.