Savoir-faire is a canonical phrase meaning that one knows how to do something. It does apply to knowledge, but more for hands-on knowledge or skill than general knowledge, as faire does mean “to do”. So as you pointed it our, it’s like “to know what/how to do”.
Savoir-faire is used as noun only and can be understood as a set of skills or general knowledge of what to do in a situation.
Although is can be used as is in English, I think the more appropriate translation and concept in English is know-how, but savvy is also in the right direction.