This is still to be discussed but most studies mention the intake of 50-100 mg/day. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3136969/ mentions 75mg, https://en.wikipedia.org/wiki/Zinc_gluconate#Zinc_gluconate_... is a good starting point for further research.

But as always, consider every supplement carefully. I took 50mg a day before and noticed some inconvenient side effects like bad odour of my sweat and very dry skin. ATM, I just take 50mg/week, and I didn't experience a cold in the last two years (for whatever reason).