Do Kings Still Wear Crowns?

Kings didn't just wear crowns on a daily basis ever. Most of the crowns you are thinking of are coronation or state crowns anyway, so they're only worn during coronations or state occasions/portraits.

Which Monarchs still wear crowns?

Today, only the British Monarchy and Tongan Monarchy, with their anointed and crowned monarchs, continue this tradition, although many monarchies retain a crown as a national symbol.

Do kings have to wear crowns?

Crowns have always been for ceremonial occasions only. No king that I know of wore a king as everyday wear: it was much more for formal occasions when the king wanted to express his dominance.