Mi mentora me llamó para aclarar la duda.

Mentora is the feminine form of mentor. Spanish nouns and many job titles change form to match the person’s gender:

• male mentor: mi mentor
• female mentor: mi mentora
  In many Latin American contexts, you’ll hear both, but mentora is common and clear when the mentor is a woman.

Me is an object pronoun meaning me (the person receiving the call).
Mi mentora me llamó literally = My mentor called me.
Spanish often uses these small pronouns before the verb instead of repeating the noun:

• Mi mentora llamó a Carlos. (called Carlos)
• Mi mentora lo llamó. (called him)
• Mi mentora me llamó. (called me)

When the object is a noun/name, Spanish uses the personal a: llamó a Juan.
But with object pronouns (me, te, lo/la, nos, los/las), the a disappears because the pronoun already replaces the whole a + person phrase:

• Llamó a Juan → Lo llamó
• Me llamó already contains the idea of “called + me”

Llamó is preterite (simple past) for he/she/you(formal) called.
The accent in llamó is required and also helps distinguish it from other forms:

• llamo (no accent) = I call / I’m calling
• llamó (accent) = he/she called

In Latin American Spanish, llamar commonly implies a phone call in context, and me llamó is very natural for called me (on the phone).
If you want to be extra explicit, you can say:

• Mi mentora me llamó por teléfono.
• Mi mentora me llamó al celular. (on my cell phone)

Para + infinitive expresses purpose: in order to / to.
So me llamó para aclarar la duda = she called me to clear up the doubt/question.
If the subject changes, you typically switch to para que + subjunctive:

• Me llamó para que yo aclarara la duda. (she called so that I would clear it up)

Aclarar la duda means to clear up the doubt / to resolve the uncertainty. Very common alternatives:

• resolver la duda (resolve the doubt)
• quitarme la duda (take the doubt away from me / put my mind at ease)
• aclarar una duda (clear up a doubt, more general)

They overlap but aren’t the same:

• pregunta = an actual question you ask
• duda = doubt/uncertainty (the thing you’re unsure about)
  You might say Tengo una pregunta when you want to ask something, and Tengo una duda when you’re expressing uncertainty and want clarification. In many contexts, tengo una duda is the more natural Spanish way to introduce a “question” you have.