Hello, first of all thank you so much for arranging this Game Jam.
I had a question, regarding the public repository. Is sharing the code and the assets mandatory if we want to keep the assets private?
Thank you, hope you all have a great jam ahead!

The jam is hosted by GitHub so I assumed they want you to share the assets of the game so other can contribute or learn from it. 
However, it's possible to public the repository only during judging period and private it after the results came out (not sure about any specific rule regarding this).

Sending the Assets is probably not mandatory, as some licenses for assets require you not to release them publicly, and uploading them to GitHub would be releasing it.  However, the source code you write is mandatory I believe.

The rules say:

"Create a new public GitHub repository to store the source code and any assets you’re able to share for your entry and push your changes before December 1 13:37 PT."

So, if you have assets that you can't share (e.g. because you're bought them and aren't allowed to redistribute them outside of your game), you don't need to add them to the repository. But if you *can* share them, my read is that you need to do so,

Thanks to all of you for your insights, I wish you all best of luck for the Jam.