Sugs,
The information is in the aerad enroute supplement (yellow), com section. All the frequencies for each airfields nav aids are given, along with the type of modulation - for example all the locator beacons for CDG are listed as A1A. The explanatory notes on com page 1 has a long explanation of NDB emissions and when to use the BFO which I won't try to reproduce here, but as has been stated previously most french NDBs are A1A or N0NA1A and need the BFO to ident them.
Hope that helps. Now that you know you could ask the line trainer the same question at the start of the check. If he/she doesn't know then they could be kept busy for hours on the jump seat searching through the ops manuals and thus not notice what you are doing wrong in the mean time.