Here's the breakdown:
* Joh: This is a relative pronoun, introducing a relative clause.
* tez bhaagega: This is the verb phrase, meaning "will run fast".
* wahi: This is a demonstrative pronoun, specifically a demonstrative adjective pronoun. It's used to point out something specific, in this case, the person who runs fast.
* jeetega: This is the verb, meaning "will win".
So, the sentence means "Whoever runs fast, he/she will win."
"Wahi" is the pronoun that stands in for the person who runs fast. It's similar to using "he/she/they" in English.