Which engine oil can be used in g13b engine?
The answer is in the owners manual. Sometimes on the oil cap itself. Just a guess either 5w-30, or 10w-30.
It is your vehicle so you can use anything you want. But a simple web search shows 5W30 and it only took less than a minute to find that .
5W30 or 10W30. https://www.engine-specs.net/suzuki/g16b.html