To determine how many shots on goal Ruthie took, we start with the information that for every 7 shots, she scores 2 goals.
First, we find out how many sets of 2 goals are in 8 goals:
\[ \frac{8 \text{ goals}}{2 \text{ goals/set}} = 4 \text{ sets} \]
Since each set requires 7 shots, we multiply the number of sets by the number of shots per set:
\[ 4 \text{ sets} \times 7 \text{ shots/set} = 28 \text{ shots} \]
Therefore, the total number of shots on goal that Ruthie took is:
\[ \boxed{28} \]