Can I use my iMac 2 as a monitor for my iPad Pro?

Target Display Mode was a feature of some old iMacs released between 2009 and mid 2014. Of those, only 24" and 27" iMacs released in 2009 or 2010 could accept regular DisplayPort input. There was a later 21.5" price-point that lacked Thunderbolt, but whether it supports TDM using DisplayPort input, or doesn't support TDM at all, is unclear. Apple has never addressed that special case in their support article.

Apple also added some restrictions on the video source over the years. Now that source must be a Mac released in 2019 or earlier, running Catalina or earlier.

Use iMac as a display with target display mode - Apple Support

So if you connected an iPad with USB-C (DisplayPort) output to a 24" or 27" iMac from 2009 or 2010 with a USB-C to Mini DisplayPort adapter cable, things might not work at all. If they did, it would be "Christmas".

AirPlay to Mac (which Mr. Jones described) is another possibility, if you can meet the system requirements in

Continuity features and requirements for Apple devices - Apple Support

I know of no model known as a "iMac 2" so cannot give you an answer at this point.

Please do "About this Mac..." from your Apple menu and tell us what that shows for model, sub-model, and macOS versions. Samples showing those:

Newer Macs and iPads can use Airplay to Mac to put the iMac display on your Mac's screen. Does not ork with older Macs and macOS versions. Info here:

Stream video and audio with AirPlay - Apple Support

As you see, without a more precise description of your iMac, we are a a standstill.

No

If you have a relatively new iMac you can use airplay to Mac. Otherwise, no