Qenya
káro
noun. doer, actor, agent
tyaro
noun. doer, actor, agent
There are more words but they are from Tolkien's earlier conceptional periods. Tolkien likely changed these words as he evolved the aesthetics and completeness of the languages. You may even find languages that Tolkien later rejected. Do not mix words from different time periods unless you are familiar with the phonetic developments.
Below: Tolkien's Late Period (1950–1973). These are from Tolkien's late conceptual period — his most settled forms of the languages. Prefer these over the earlier ones above when composing new text.
A noun in The Etymologies of the 1930s glossed “doer, actor, agent” derived from the root ᴹ√KYAR “cause, do” (Ety/KYAR).
Conceptual Development: In an earlier version of the entry for ᴹ√KAR “make, do”, Tolkien had ᴹQ. káro “doer, actor, agent” (Ety/KAR; EtyAC/KAR), but this form was abandoned when Tolkien decided ᴹ√KAR meant only “make, build”.
Neo-Quenya: Despite the later restoration of the sense “do” to the root √KAR, I would stick with attested tyaro for “actor, agent”, since Q. tyar- “cause” continued to appear in Tolkien’s later writings.