Risotto figures out that Doppio must be a Stand user that the boss trusts in deeply because he’s able to hear the noise from a certain Stand. Risotto then uses his Stand Metallic against him. Metallic is able to control magnetic force and attacks Doppio. Doppio uses the part of the boss’s power he received from him. While they’re fighting, Risotto realizes that Doppio’s personality and actions seem to be changing and he realizes exactly who Doppio is.
Yes, this had already been confirmed 
in 16th century Germany.
أجل، لقد تمّ تأكيد هذا بالفعل في القرن
السّادس عشر في ألمانيا
Ja, das wurde schon im 16. Jahrhundert
in Deutschland berichtet.
Sí, existen registros
desde el siglo XVI en Alemania.
Sí, existen registros
desde el siglo XVI en Alemania.
Sì... questo fenomeno era già stato individuato 
nella Germania del sedicesimo secolo...
É algo que já havia sido descoberto
na Alemanha, no século XVI.