Finding C and D on the keyboard: https://www.musictheory.net/exercises/keyboard/ydyyyynbynb
Practice reading C and D on the Treble Clef (right hand): https://www.musictheory.net/exercises/keyboard-reverse/bg8yryybnynyyyy
Practice reading C and D on the Bass Clef (left hand): https://www.musictheory.net/exercises/keyboard-reverse/nmcyryybnynyyyy