'Where' and 'wherein' function as interrogative adverbs.
'Where' is used to ask about the location of something or someone.
'Wherein' is used to ask 'in what place or respect.'

'Where' and 'wherein' can also be used as relative adverbs. Relative adverbs describe a noun or noun phrase.
We use 'where' to express location.
We use 'wherein' to express the meaning 'in which.'

'Where' is one of the most used words in the English language. 'Wherein,' however, is old-fashioned and informal. 'Wherein' is mostly used in humanitarian articles.

'Where' and 'wherein' may be similar in their parts of speech and appearance; however, they cannot be used interchangeably as they express different meanings.