Hello rikki18, welcome!

I just look at watermarks when I have to. I think as you do more and more of them over time you will get used to it and become more poficient at it.
I am not sure of Germany but some watermarks can be recognized without using fluid, or just wetting with water (for used only).
I think scanning the watermark (with fluid) and then using the scan to compare to a catalogue is a good idea as otherwise you have to remember hat you've seen when you look at the catalogue and try to find the correct one. Maybe not always but how does one tell a sideways watermarks or upside down quickly? Experience I think.