I too was perplexed by the SSR codes question in my CFPA exam last week having never seen nor read about them when studying.
So I took a stab in the dark and got the answer wrong.

3 items had to be matched to the codes /S, P, D, M, J, E as per the Supplementary Information diagram off the Flight Notification Form.

1 First aid kit
2 Water
3 ELT 406MHz

Only after the exam was I able to find the info in the AIP as per the attached photos.

The Flight Notification Form is under Appendix 1 in the AIP ENR 1.10-13
Supplemental Information - Item 19 ENR 1.10-30 & 31

It may seem odd for the examiners to dig a question out of the depths of the AIP like this but I guess if they have asked it then we had better know it.

I passed with 82%, my lowest of the 4 sat since September but am very happy as it was the toughest so far.
CMET in 2 days time