Can someone communicate without knowing literacy skills?
One way to communicate would be through the use of gestures. A person could make gestures using his or her hands. Pointing to things is an obvious example. Tourists in foreign countries can indicate what they want by pointing. Making a gesture with one's hand toward one's mouth might indicate that a person was hungry. Holding the index finger to one's lips might communicate that the person wanted another person to be quiet.
We can also make communicative gestures by moving our heads in a certain direction. Nodding the head up and down indicates assent or agreement, while shaking the head back and forth from left to right can indicate disagreement. Moving the head in one direction left or right could indicate that the other person should look or move in that particular direction.
We can also communicate through drawing. Consider, for example, the famous drawings on the walls of certain caves in France or even the game of Pictionary.
Certain non-verbal sounds might also be used to communicate, such as whistling (to attract someone's attention), humming, or imitating the sounds that certain animals make (moo, buzz, hiss).