If it's a saved swatch, you should be able to do the following:
- Go to the Swatches panel (Window > Swatches)
- Double-click on the swatch (or with the swatch selected, go to the Swatches panel menu in the upper right and select Swatch Options...)
- In the Swatch Options dialog, change Color Type to CMYK for the CMYK values or Web Safe RGB for the Hex values