know one's stuff

Also, know one's onions. Be experienced or knowledgeable in one's field or in the matter at hand. For example, Patrice knows her stuff when it comes to Mexican history, or We need a handyman who knows his onions. The allusion in the variant is unclear. [First half of 1900s]

Common Names:

Name	Pronounced	Usage
Desideria	-	Italian, Spanish, Late Roman
Armstead	['a:msted]
Veceslav	-	Medieval Czech
Paige	[peidʒ]
Constantijn	kawn-stahn-TIEN	Dutch
Roxie	RAHK-see	English