Question

Sh! someone -------------------- to our conversation. (listen)

[fill in the blank with the correct form of the verb given in the bracket]

Answer 1

~Hello There!~

This appears to be a present tense sentence
Therefore it would be 'is listening'

Hope This Helps You!
Good Luck :)
Have A Great Day ^_^

- Hannah ❤

Answer 2

Someone is listening to our conversation this is the answer.