The only way to do that is to know the source! - or phone the MS Activation Center and ask them to check.
If you got the stuff from eBay or similar site, and/or it's a Retail license, then it's almost certainly counterfeit.
If you bought it from a reputable dealer, then it's almost certainly genuine.
If you want to ask MS to check, then all they can do is check to see whether the license has been issued (they may also be able to say whether it's already been activated - but you may need to get a Supervisor to do that). That's no guarantee that it
may not be revoked at some future date.
Use the link to your local Activation Center from this list...
https://www.microsoft.com/licensing/existing-customers/activation-centers.aspx