2007 frontier sudden loss of oil

Hello, if you are certain you do not have any oil leaking externally, it could be getting consumed by the engine. Removing one or more spark plugs and checking for oil fouling would be one way to check. Checking for any blue or dark smoke coming out of the exhaust at times can be evidence of oil burning also. Ensure the PCV system of the engine is free of restriction. Beyond that, professional guidance is needed to determine the source and severity of the concern.