Which is the correct duration of an AES execution? I  want to verify if my trigger gives me the correct duration of an AES-128 execution in a specific chip; I need only to have the duration of an AES block encrypt without any other functionality.

The frequency of the CPU is 128 MHZ, the frequency of the AES execution is 64 Mhz.

How can I calculate the duration of an execution of AES in order to verify with what I found with my oscilloscope?
The duration will depend on the chip and on the implementation.

In a good implementation, the duration of encryption is independent of the combination of the secret key and the message to encrypt (otherwise a so-called timing attack to gain knowledge on the key and/or the message is possible).

You need a model of the chip and its cache and the assembly code to do some real estimates (usually giving you a range of minimal and maximal cycles needed). For tight bounds there are commercial offers, e.g., by Absint. It is a feasible, but not a trivial task.