I heard a saying of the ulama that if you find a snake in your home you should warn it 3 times before killing it because it may be a jinn. What is meant by the warning in this case, are there specific words to be said or is it a general warning with the mention of Allah in any language?

Ustadh AbdulAziz al-Haqqan

The warning is that you tell it to leave and not appear to you or harm you, three times, and no single fixed wording is required, the scholars transmit more than one form of it. Are you asking because you see snakes in your house?