"watashi wa dansu wo benkyou desu" is not correct.
As for "I take dancing classes", you say in Japanese; watashi wa dansu kyoushitsu ni kayotte imasu.
(class)
And, for "I'm learning dancing", you say; watashi wa dansu wo naratte imasu.
"watashi wa dansu wo benkyou desu" is not correct.
As for "I take dancing classes", you say in Japanese; watashi wa dansu kyoushitsu ni kayotte imasu.
(class)
And, for "I'm learning dancing", you say; watashi wa dansu wo naratte imasu.