If you're using "learned" as an adjective (meaning "having or showing knowledge"), there isn't a perfect homonym. However, "earned" can be used in a similar context to mean "obtained through effort or merit."
If you're using "learned" as a verb (meaning "to acquire knowledge"), the homonym is "burned."
Here are some examples:
* Adjective: "She is a learned woman." (meaning she has a lot of knowledge) - You could replace "learned" with "earned" in this sentence to mean she gained her knowledge through hard work.
* Verb: "He learned a new skill." (meaning he acquired a new skill) - This sentence could be replaced with "He burned the midnight oil" to indicate that he put in a lot of effort to learn the skill.
It's important to consider the context of the sentence when looking for a homonym, as it can influence the best word to use.