juki

One root. Nothing to take apart. Juki is not ju- plus anything, and the j is the consonant of English yes, so it is said "YOO-kee". It joins the small set of bodily-sensation verbs the course has been collecting: senti at 139, dolori for hurting, juki for itching.

The grammar is where learners slip. In Esperanto the thing that itches is the subject, exactly as in English: la haŭto jukas, the skin itches. The person is not the subject and the verb takes no object, so mi jukas says that you are the itchy surface, which is occasionally what you mean and usually not. To put the person in, use a dative-ish al: la brako jukas al mi, the arm itches me. The transitive twin jukigi is to make something itch, which is what a wool ĉemizo does, and juko as a noun is the itch itself.

The answer to an itch is a different verb. Grati at rank 2,423 is to scratch, and it is transitive: you scratch the arm, mi gratas la brakon. So the full sentence a doctor says is ne gratu, eĉ se jukas. Beside them sit the causes: insekto at 1,473, piki at 1,446 for the sting, and haŭto at 1,300 for the surface it all happens on.