How can I try to boot a completely stuck Macbook Pro?
It could be something as simple as the MagSafe DC board or it could be the whole logic board. See below:



Normally, I wouldn't recommend that a user change out this part as Apple goes out of their way to make a complex assembly, but since you have an oscilloscope on your workbench....

The part is relatively inexpensive as compared to a logic board and I have fixed MacBooks where this component has failed.  Ifixit has excellent tear down instructions on how to get at this component.

You didn't specify which specific model, so I grabbed the 2013 model for reference.  The link is:  https://www.ifixit.com/Guide/MacBook+Pro+15-Inch+Retina+Display+Early+2013+MagSafe+DC-In+Board+Replacement/17055.

If it isn't the right model, you can find the correct one on their site.  I hope this helps...