Step 1: Understand the meanings of the options.
Omnipresent means present everywhere.
Omnipotent means all-powerful.
Omniscient means all-knowing.
Optimist means a person with a positive outlook.
Step 2: Match the definition.
The phrase “one who knows everything” directly refers to someone who is all-knowing.
Step 3: Conclusion.
Therefore, the correct word is Omniscient.