见

The xiàn reading is older. Before 现 was created as a separate character, 见 did double duty: 'to see' (jiàn, active) and 'to appear / be seen' (xiàn, passive — what shows itself to the eye). When 现 took over the passive sense in everyday use, only a handful of classical phrases preserved the xiàn reading on 见. The two characters are still synonyms in this sense.

You meet 见 almost only in frozen classical material: the grassland line 风吹草低见牛羊 (Northern Dynasties folk song), the set phrase 见头角 ('to first show one's talent'), and a few Confucian quotations. In all modern writing — including modern translations of those very same lines — switch to 现. Default reading of the bare character is always jiàn unless the surrounding text is explicitly classical and the meaning is 'appear'.