My ram speed is 2666MHz but speccy shows wrong ram speed?
Both would appear to be correct, actually. Keep in mind that essentially all memory in use today for computers (certainly computers that can run Speccy :) ) is DDR, or 'double data rate' memory. More info here: https://en.wikipedia.org/wiki/Double_data_rate
In short, though, the speed listed for DDR is an 'effective' speed, as DDR memory can update on both the rising and falling edges of the clock signal, in other words, at 'double' the clock 'rate'.
What Speccy is reporting is the speed of the clock signal, which should, thus, be approximately half the speed the DDR module is rated for. (This does seem to be very, very slightly low, as half of 2666MHz is 1333MHz. It's possible that your computer is clocking the memory ever-so-slightly slow, but this wouldn't cause any impact that a person could notice. It could also be an issue in regards to how it's being measured/reported.)
As for the 'Unknown' part, that suggests to me that you have DDR4 memory, which Speccy is not currently configured for - please accept our apologies for any inconvenience that this may cause.
Maybe it's being reported so low because it's in the wrong slot for using a single channel stick of RAM - just a guess.