Yellow cosmos flower is not a single flower. Group of flowers look like a single flower. Such inflorescence named as Head or Capitulum.
Outer flowers are ray florets and flowers in the centre are disc florets. I separated disc floret bifid stigma and observed under foldscope. This flower is pollinated. You can see pollen grains on bifid stigma.

Pollen grains on bifid stigma of disc floret