What Mark Kramer said about saying "Learn on!" is true, but I really agree that it would be a bit odd to say this generally. "Learn on" is not a construction I've really heard outside of the "on" denoting the thing you are using to learn. For example... "Languages are easy to learn on the computer." If you wanted to denote ongoing learning, you would just say, "I'm learning English." or for continuing the action into the future, "I'm going to keep/continue learning English." * You could also say, "I'll go on learning... (until I understand/ until there is nothing more to learn/ until I die... etc.)."

"On" here refers to an ONgoing action. In an Imperative sentence: Learn on! Which means: keep on learning! Like "Go on!" P.S. I don't think "Learn on!" is something I would be inclined to actually use in practice. It sounds a bit constructed, even though it's grammatically correct.

i think: LEarn is just the verb.. which you use when you say that you want to know about something... "i'm going to learn another language". when you use Learn on i think is used when you are learning something... and you go on learning that... i hopa i can help you a bit