For kinematics, we use the URDF format from ROS along with the kinematics (and motion planning) features from the ROS Moveit plugin. Here‘s the ROS code for Niryo One where you can find all those info.
For the simulation on Niryo One Studio: you can follow this tutorial (method 1), deactivate all motors, and reboot the robot. You’ll still see the robot moving in the 3D view but the real robot won’t move. Note that this is a “semi”-simulation mode, as you still need to power on the robot.
You can also (better to do that) run the simulation on your computer (see the Niryo One ROS repository), and use either your own code, or Niryo One Studio (then, you’ll need to choose “localhost” as the IP if you run the simulation and the desktop app on the same computer).