A biography on Pope Francis would typically be classified under the Dewey Decimal number 282.092, which is the section for biographies of Roman Catholic popes.
I would guess the Dewey Decimal classification for a yearbook is 051, English language serials.
Dewey was born on 10 December 1851. His book was published before April 1876. He would have been 24 at that time. Lydenberg, H.M. Dewey, Melvil. Dictionary of American Biography. New York: Charles Scribner's Sons, 1944. Suplement I; pp 241-243.
It's a Dewey decimal number. This book would be about arithmetic.
You would look under the number 394.266 for books about Christmas feasts and festivals in the Dewey Decimal System.
Sharks would typically be classified under the Dewey Decimal System number 597.3, which covers topics related to cartilaginous fishes, including sharks, rays, and skates.
The Dewey decimal number for Lego's would be 688.72. This classification is used for books and resources related to toys made of plastic blocks, such as Lego's.
915 is the Dewey decimal classification for Asia (which would naturally include Hindus). 950-959 covers the General history of Asia.
Native American music is classed under 788.3
Twitter as a social media platform does not have a specific Dewey Decimal Classification number since the Dewey Decimal system primarily categorizes physical books by subject matter. Social media platforms like Twitter would not typically be found in library collections using the Dewey Decimal system.
There are a number of saints named Francis. Please be specific.
It depends on what you are looking for. Masks in cultures would be the 390's. Photo books of masks, masks in theater, how to make masks, etc would be mixed through the 700's.
A book on optical illusions would likely fall under the Dewey Decimal Classification number 152.14, as this section covers works on visual perception and visual illusion.