A mis sobrinas les gusta tocar la guitarra.
This is talking in plural form. Also, jugar means to play (like playing with toys,), but in this case you would say tocar. In English play can mean different things, but you need to remember when to use each.
Answer:
The answer is Ustedes <u>saben</u> que hay examen hoy?
Explanation:
I don’t know which conjugation you wanted but here’s a chart
