quite easy
longest element is roughly a halfwave
real reverse engineer would be
add a reflection bridge to tx port of lime
do a tx sweep out of that port
with rx port connected to forward and reverse port of the refl. bridge you have an antenna analyzer …
now you can do a swr sweep and see the yagi resonance
homebrew a reference antenna (say a halfwave dipole)
place it away several wavelength distance
now you can calculate the gain of the yagi (and measure directivity, front back ratio etc etc.)
that would be real reverse engineering 
… but i am guessing you just wanna know where you can use that yagi (as an rx antenna) … the rule over the thumb (longest is halfwave) is good enough