Grbl is software for controlling the motion of machines that make things. If the maker movement was an industry, Grbl would be the industry standard. Most MakerBots and open source 3D printers have Grbl in their hearts. It has been adapted for use in hundreds of projects including laser cutters, automatic hand writers, hole drillers, graffiti.
Ralph, the only reference to this 'stock board' you mention that I could find is one AliExpress seller:
https://www.aliexpress.com/store/product/GRBL-0-9J-USB-port-cnc-engraving-machine-control-board-3-axis-control-laser-engraving-machine/1941516_32713561151.html
This isn't really a common board, and if there is no documentation for it it will be difficult for us to assist you.
The standard grbl limit inputs are on D9 (X) D10 (Y) and D12 (Z). See https://github.com/gnea/grbl/wiki/Connecting-Grbl
There are pins on the header that seem to be labelled A0-A7 and D13 - and the diagram on the above linked page tells you what those are used for.
I can also see some with labels starting with X/Y/Z but I can't make out the labels clearly. At a guess I'd expect those to be the ones you need for the limits. Can you tell us what they say? Maybe a close up photo from front and back of PCB near that connector would help us.
If you have a multimeter, it would be possible to use that to trace out the connections from the ATmega IC to the header pins as suggested by @luben111
All that said, this board uses a CH340 USB to serial chip, and this has been known to be the cause of communication problems for many people (data loss). I would personally recommend getting a board that is more common and well documented, such as the Protoneer shield, and an Arduino Uno to plug it into. I expect those stepper drivers on the Woodpecker board follow the standard 'Pololu' pinout, so you should be able to move them across to a new shield. After all the time and cost invested a CNC, you really don't want to use an unreliable and unsupported controller, even more so as a beginner.