The correct answer is 2. Proofreading your work is really important.
Step-by-step explanation:
A sentence is considered as correct if all words on it are written correctly (spelling), and all the elements express a complete idea following language and writing conventions (grammar).
According to this, from the options given the correct sentence is "Proofreading your work is really important" because in this sentence every word is spelled correctly, including the word "proofreading" that is misspelled in other options.
Besides this, the sentence is grammatically correct, especially because this includes the word "your" rather than "you're" considering in this context it is necessary to use "your" because it refers to a possessive pronoun (your work) rather than to the subject "you" and the verb "are" as "you're".