How can I retrieve data from my iMac's SSD drive?

The 2009 iMac did not come with SSD storage internally, only magnetic hard drives. So if your iMac now has an SSD internally, it would have been a third-party unit installed by someone later. In any case, yes, you should be able to pull the SSD from the iMac and mount it in an external drive case, if that's what you mean by "disk caddy". It will need to offer a serial ATA interface.

If that's not what you meant, please explain further.

Regards.

I am assuming you never backed up using Time Machine ?, if not then just remove the drive from the computer , put it in an enclosure and copy to another Mac.r

Yes! If you remove the stock 3.5" hard drive from the 2009 iMac..?

You can use a USB to SATA adapter or a USB Drive Dock.

see > usb to sata 3.5 hard drive adapter

or a > usb drive dock

Did somebody install an SSD?

Maybe pull the drive>

https://eshop.macsales.com/installvideos/imac_late27_2009_hd/iMac10-1-27/

Yes, here's a universal one, used to see them for $7...

https://www.amazon.com/SATA-Adapter-Converter-Cable-Drive/dp/B01HO07GNW