How can I give a questionnaire to those who have recovered from COVID-19 disease .. for any country of science?
Through the hospital they are discharged would be the easiest.
But I think this may need ethics committee for approval before the conduction of such study
The hospital can be a good source to get the patient's information. Normally, it is convenient when they are being treated in the hospital. At the end of their treatment if you give them the questionary as the anonymous format, patients participate well. Better you can collaborate with a different researcher with similar interests and in different countries, let them negotiate with the hospital authority to collect data before discharging patients after recovery.
I agree with the previous answers that the best way is to collect data from the source and these would be the hospitals who treat COVID-19 patients. But as mentioned, these hospitals will most likely require you to have ethics clearance and informed consent as the target participants are considered as belonging to vulnerable groups. Another option is to look for a Facebook community support group of COVID-19 recovered patients. Proper way is to ask permission from the community manager along with the ethics clearance. Good luck on your study.