For this case, the important thing is to identify the verb of the sentence.
We have then that the verb in English is:
Understand.
The verb conjugation in English is:
I understand
you understand
he / she / it understands
we understand
you understand
they understand
The conjugation of the verb in Spanish is:
Yo entiendo
Tu entiendes
El/Ella entiende
Nosotros entendemos
Ustedes entienden
Ellos/Ellas entienden
The sentence translated in English is:
I do not understand the problem
Answer:
The verb of the sentence is:
entender
