You can get concentration in the cell using the following code:
C_YI(c,t,0)*C_R(c,t)
C_YI(c,t,0) will give you mass fraction of the component. C_R(c,t) will give you density of the phases in the cell. Hence multiplication of the two gives you the concentration of the component (whose ID is 0) in the cell.
where:
c is the cell identifier
t is the thread identifier
0 is the ID of the component. If it is first in your Materials > mixture-template > Mixture Species > names Edit list then its ID is 0. If it is second in the list then its ID is 1.