Hi Ilias,some time ago I wrote to Nikolay Tzankov - an expert on green lizards from Bulgaria.He told me some keys on identification of the subspecies trillineata/dobrogica.
The last(outter most) row of ventral scales in L.t.trilineta are more elongated(width about 1/3 of the lenght),while in L.t.dobrogica they are shorter.Besides,head proportion to body is different in both subspecies - in trilineata it's 'lighter' buid,more slender than in dobrogica.Also no blue spot on neck (or very light one)in trilineata.So,based on that I think this one is L.t.trilineata.

P.S. Nikolay also told me that biochemically both subspecies are with a species status but that needs further research,I guess! 

Hello Ilian!
Well, in Greece there are more ssp than those you wrote ;-)
The most possible ssp for Naxos is Lacerta trilineata citrovittata Werner, 1935, but I haven't seen any records about it. 

Ilias, citrovittata is supposed to be Tinos, Syros, Andros only. Typically, other islands probably are the same or something in between (cf. Elaphe quatuorlineata scyrensis). 

Jeroen said: "citrovittata is supposed to be Tinos, Syros, Andros only"

and Mykonos too. Naxos is quite near to Mykonos (see http://z.about.com/d/goeurope/1/0/y/t/1/cyclades-map.png )
but I haven't got any reports from Naxos. 

> and Mykonos too.
Source? 

this book http://www.herpetofauna.gr/gallery/image/Vivliografia/EllKypBIG.jpg
by Ioannidis and Dimitropoulos, but it has much data that is old now and has changed...