Your iPad9 fundamentally does not support Thunderbolt. As such, if purchasing an external monitor to be used specifically with your iPad9, you will potentially incur significant and unnecessary cost.
Your iPad9 has a Lightning port - to which you can connect an appropriate HDMI (digital - recommended) or VGA (analogue) video adapter. Your monitor will obviously need a video connection that supports one or other of these two video standards.
Apple's Lightning to HDMI or Lightning to VGA Adapters both have a Lightning pass-through power connector - to which you can connect your iPad's Power Adapter:
Connect iPad to a display with a cable - Apple Support
- Lightning Digital AV Adapter (HDMI)
https://store.apple.com/xc/product/MW2P3ZM/A
https://store.apple.com/xc/product/MD825ZM/A