The Nexus 9 USB drive is using the Google USB driver. You can find the driver on this website located here. You should download the latest drive in order for this to work. Below you can find the process of installing this driver onto your computer and connecting the Nexus 9 mobile phone to your computer so you can transfer files to and fro from your mobile device.
Nexus 9 USB Driver
Download the Google USB driver from this website and extract the file to a directory onto your computer. The file is normally called (latest_usb_driver_windows.zip). Now you will need to open your device manager in order to update the driver for the device which would normally be showing an error.
1. Click Start menu and right-click on Computer.
2. Click Manage.
3. Click Device Manager in left pane.
4. In Device Manager window, expand categories and locate the device
5. Right-click on the device name and select Update Driver Software
6. Click on Browse to find the location of the downloaded driver file.
7. Find the files you had just extracted for the Google USB driver and click on the .inf file;
8. Click on Next button to install the driver.