To find the percentage of cupcakes that had sprinkles, we first need to determine the total number of cupcakes. Oscar bought 92 cupcakes with sprinkles and 8 cupcakes without sprinkles.
Now, we can calculate the total number of cupcakes:
\[ \text{Total cupcakes} = 92 + 8 = 100 \]
Next, we find the percentage of cupcakes that had sprinkles by using the formula:
\[ \text{Percentage} = \left( \frac{\text{Number of cupcakes with sprinkles}}{\text{Total number of cupcakes}} \right) \times 100 \]
Substituting the values we have:
\[ \text{Percentage} = \left( \frac{92}{100} \right) \times 100 \]
Calculating this gives:
\[ \text{Percentage} = 92% \]
Thus, the percentage of the cupcakes that had sprinkles is
\[ \boxed{92%} \]