Which version of camera raw should I install?

Photoshop cs6 can only use up to camera raw 9.1.1, so if you have a newer camera that photoshop cs6 won't open because a newer camera raw plugin is needed, most likely you can use the Adobe DNG Converter to convert the camera raw files to dng copies which then photoshop cs6 should open.

https://helpx.adobe.com/camera-raw/kb/camera-raw-plug-supported-cameras.html

https://helpx.adobe.com/camera-raw/digital-negative.html

If in photoshop cs6 you go Help<About Plug-In>Camera Raw, what version does it say?

https://helpx.adobe.com/camera-raw/kb/camera-raw-compatible-applications.html

9.1.1 (See Note 5 and Note 6)