You have a notebook that is shared and you are on the machine where the
notebook is shared [NOT the machine where the actual folder resides].
For example Desktop (where notebook folder is stored) laptop (where notebook
is shared)

Everything is working and both are syncing fine.

Now if I am not in the office and connected to the network and I close the
notebook in the laptop, is there a way to open the notebook again.
I have tried but I can't find the cached copy of the notebook to open it.
I can locate a cache file in the cache location but it doesn't contain
separate notebooks.

Is the lesson I need to learn - DON'T CLOSE the notebook on the machine
where you are sharing it!
That seems to be the solution - keep all notebooks open.