I am more susceptible to covid19 because of my ckd and asthma. may i take zinc 20mg per day to boost my immune system? please help.

Yes and maybe: You are susceptible to more severe forms of the infection based on your comorbidities. Zinc has been recognized as a general immunity booster with better outcomes in some of the patients with Covid it has been used for, no outstanding scientific evidence otherwise. Dose appears to be in the 10-20 mg range, side effects being gastrointestinal and drug-drug possible interactions.