Put the cleaned onion for 10-15 minutes in the refrigerator. Volatile disulfides, creating a distinctive smell of onions and propantial, which causes tears, will not be released when cutting so much.
Sprinkle the knife with cold water from the tap. The disadvantage is that you need to wet the blade continuously throughout cutting. Otherwise, the tears will be "pouring a stream."
The third way (exotic).
Put next to a candle: volatile compounds will be attracted to a flame. Also, you can put next to a pot of boiling water (if they attract couples) or the fan - to drive them to the side.
Chew gum while cutting onions.