so if the specifications mention DNR on one product and SnR on another one and show 122db wich is better or is it a trick to sell a product that seems very the same
Ideally you want something with both a good SNR and a good DNR, although of the two, I will take DNR, as poor DNR makes everything sound a bit flat and boring; poor SNR only really rears its head at eardrum breaking sound levels.
But then, I am from the LP generation, I am used to a bit of hiss.
They are two totally different measurements.
There is no way to compare products with different measurements.
Maybe if you posted the devices you are considering, we can help you decide the better component.