To solve the problem of how many cups of candies Emily needs in total, you would use multiplication.
She wants to put \( \frac{3}{4} \) of a cup of candies into each bag, and she is filling 8 bags. The total amount of candies needed is calculated as:
\[ \frac{3}{4} \text{ cups/bag} \times 8 \text{ bags} = 6 \text{ cups} \]
So, the correct operation is Multiplication.