know where is at
where it's at
1. The place where things are most exciting, active, or lively. I've traveled all over the world, and, if you're looking for a party, Ibiza is definitely where it's at. For the last few decades, Austin has been where it's at for the independent music scene in the southern United States.
2. The place, field, industry, etc., where there is the most activity and opportunity. For people who want to produce online content, streaming services are where it's at right now. If you're looking for the most lucrative and plentiful job opportunities, computer programming is where it's at.
3. That which is currently very fashionable, trendy, or popular. Big, broad suits are so last-century—well fitted trousers, jackets, and shirts are where it's at right now. When you're building or remodeling your home, energy-saving features like triple-glazed windows and solar panels are where it's at.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
know where something is at
to know where something is located. (Without at, this sense is standard English. See also know where it's at.) Do you know where the hammer is at? I don't know where my glasses are at.
See also: know
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs. © 2002 by The McGraw-Hill Companies, Inc.