Is it possible to ask Siri to push buttons in the app with the text to speech?
I mean, I have a calculator and pushing the button of "dictation" Siri should be able to understand to push + button instead of just write inside the lable the text.
Siri cannot be used inside apps. Moreover, you can only use Siri for handling intents that are part of the
SiriKit framework, which is quite limited at the moment.
VoiceOver is perfectly capable of what you need to do. It was designed for navigating through an app with voice commands as part of the Accessibility framework.
The Speech framework as suggested by others is not available in
watchOS and wasn't really designed for voice navigation.