there is no such thing as N2KOH
u do not need to find the formula of the compound, nor the reaction in this case.
the KOH as mentioned earlier, is used to "collect" the N2.
for PV=nRT, P must be in atm(i think, in which case it would be 1 because i belieev u're most certainly talking about 760mm Hg), T must be in kelvin.
all u need to do is find out the mass of N2 based on the given data, because % composition is based on mass ratio.
so mass of N2/mass of compound = % composition of N2 in compound.