Final answer:
The yo form of the verb desayunar in the present perfect tense is He desayunado.
Step-by-step explanation:
The yo form of the verb desayunar in the present perfect tense is He desayunado. In Spanish, the present perfect tense is formed by combining the auxiliary verb haber with the past participle of the main verb. In this case, the auxiliary verb he (which corresponds to the pronoun yo) is used, followed by the past participle desayunado of the verb desayunar.
Learn more about Spanish verb conjugation