Where can I find the right protocol to be followed?
Take a look at jgm63's guide.
https://sanctioned-suicide.net/threads/n-protocol-regime-regimen-notes.27092/
Out of interest do you have any opinion on how long liquid N (unsealed, original bottle, kept in fridge) stays effective? I have one such bottle - with an expirary date of March 2019.
Most 'experts' agree that liquid Mexican vet N. will stay lethal for about 2/3 years after the expiry date if you store it well. Best is a cool place with a constant temperature. (fridge or closet.)
With time, the N. might lose some of its potency but you can tell when the N. has truly expired. The chemical components will fall apart and the liquid will no longer be perfectly clear.