What does the phrase “know or have reason to know” mean in practical terms?

Whether a party "knows or has reason to know" & should therefore be legally charged with such knowledge, depends upon the specific facts, circumstances & law involved in the legal matter.

Your question raises the issue of license revocation, but unfortunately, it does not specify what type of license was revoked & under what particular facts & circumstances. Accordingly, the definition of the phrase "knows or has reason to know" can only be addressed in very general terms.

If the revocation was, for example, the result of an offense, violation or infraction & a required legal or administrative proceeding or procedure was followed in connection with same, the revocation may have been expressly documented in records that were accessible by the licensee & notice may have also been sent to the licensee as required by applicable procedural rules or law.

Alternatively (or additionally), there may have been information or certain circumstances leading up to the license revocation, that would have lead a reasonable person to access (or otherwise become aware of) such information, or under those circumstances, to "know or have reason to know" that the license had been revoked.

It is also possible that the licensee in a particular matter may be required to present admissible & credible proof, which may have to satisfy an applicable legal standard in the revocation matter, showing that the licensee did not know, or could not have reasonably known, of the license revocation under the specific facts, circumstances & law involved in the matter. 

You should seriously consider consulting with an attorney who has experience in the area of law involved in the license revocation. Good luck.