Puzzle, Enigma
Noun
なぞなぞ
子どもはみんな謎々遊びをするのが好きだろう。
Pretty much all kids like solving riddles, right?
A puzzle puzzle is a puzzle, but it's also a riddle or enigma as well.
This word uses the kun'yomi readings of the kanji you learned, twice. You should be able to read this on your own.