It appears to be:
SUB STA No2 CAMDEN / N.J., with "REG" in the center, which would make sense on a 2 cent letter + 8 cent registry fee needing 10 cents in postage.
Add: Here is an excerpt from Postal Bulletin #4834 dated January 9, 1896 about two of Camden's stations being renamed:
Posted 06/12/2022 12:40 pm
