I am asian. i have a black spot on my penis head. i do not feel any irritation or kind of pain from it. it appears to be under the skin. please advise?

A lentigine?: What you described seems suggestive of harmless hyperpigmented macule, called lentigine, which is commonly seen in the penis or elsewhere on the body, is entirely benign, and needs no Rx. So, just watch it for next one year to see any change in its size, color, or level; if unchanged, that it is and is innate. Of course, if still in doubt, see Doc timely. Best wish...