Percent, Legend and Histogram

I don;t think it;s possible with just UI, you will need to:
1) create a new measure (press 'New Measure' in Modelling in the ribbon)
2) syntax should be something like this - you will need to adjust the blue parts

this code assumes that Annee is a numeric field, not text

% of total =
VAR varYear =
    MAX ( Table[Annee] )
RETURN
    DIVIDE (
        SUM ( Table[Nombre de Quel...] ),
        CALCULATE ( SUM ( Table[Nombre de Quel...] ), Table[Annee] = varYear )
    )

amelief,

You may use measure below.

Measure =
DIVIDE (
    SUM ( Table1[value] ),
    CALCULATE ( SUM ( Table1[value] ), ALLSELECTED ( Table1[answer] ) )
)