Let's say there is a no-name SFP transceiver without a label and without DDM support. Is there a device which is able to detect on what wavelength this SFP transmits? I have used JDSU light-meters previously and they ask user to select wavelength(for example 1310nm, 1550nm), but regardless of the selected wavelength, they will show optical Rx power.
Relying on SFP MSA is not a good options, as these specs are often faked to allow a specific switch to work with an incompatible device (I've see lots of bidirectionnal SFP which are identified as standard Single Mode SFP just because the switch was not bidir-compatible)
plugging another known SFP in front of the unknown device can give random results, and will not really help.
Using an OTDR will give you the answer, But it's quite expensive if you don't have one.
You can also use a Portable Optical Power Meter where the frequency is settable. it cost approx USD50 and it will give your the answer (and will also be really useful for debugging aso.)