Hi guys, is there any ways we can use to tell if the pressure is at 9 bar without using the pressure gauge?

In short, no..

You could taste the end result and everything. That might give you a clue as the machine is in proper working condition (right temperature right pressure etc). But you can never know the measurement of the pressure without a gauge.

What exact machine?

How do I check brew pressure without a gauge? offers suggestions, but it's worth eliminating guesswork by building your own portafilter adapter gauge. There's several threads describing how to build one, including the particularly original solution Zero cost adapter for portafilter pressure gauge.