No, Manu is not correct. He should look for the greatest data value on the number line that has any dots above it. This value is the greatest number of books read.
In this case, the greatest number of books read is 15, as it is the highest value listed on the number line with a dot above it, even though 12 has the most dots (6 dots). The question is asking for the greatest number of books read, not the most common.