The game's save and log files are located in these locations.

Windows: %USERPROFILE%/AppData/LocalLow/jakai/tentikun
or: C:\Users\YOUR_USER_NAME\AppData\LocalLow\jakai\tentikun

Linux: ~/.config/unity3d/jakai/tentikun/

On Windows copy the provided text line into the Windows Explorer address bar (see image below) to quickly jump there. The Player.log file is what I will need when you report a bug. It is best to copy this file as soon as you encounter the bug. The file is overriden when you restart the game so the logs with info about the bug will be gone if you restart. You can either share this file via a file sharing service (since you can not upload here) or copy-paste its contents into your post or join the Discord Server and upload the file there.