There are three types of neutrinos known today. When detecting them, how can we tell which type we are detecting?
Neutrino flavor is defined as agreeing with the flavor of the charged lepton participating in the interaction, so that the neutrino in the reaction $$ \nu + A \to \mu + X \,, $$ is defined to be a muon neutrino and the one in $$ \nu + n \to e + p $$ is a electron neutrino by definition.
We have no way of knowing the alleged flavor of a neutrino participating in a neutral current interaction.
As a matter of experimental fact electron and moun neutrinos (and anti-neutrinos) are easy, but tau neutrinos are much harder because demonstrating that you have a tau-lepton is hard, but both OPERA and IceCube can do that (to chose currently running experiments).