If someone is in the bathroom for a long time, and someone needs to ask them a question how are they able to respond (i.e. can they speak normally?)
According to the Talmudic halachah, it is not permitted to speak in a bathroom. See Berachos 62a and Rashi, and see Rambam, Hilchos De’os 5:6 and Rema 3:2, and numerous other poskim (see Be’er Heitev 2; Levush 2; Mishnah Berurah 3:4).
However, for a need, it is permitted to speak (Torah Lishmah 24), and this is particularly true concerning the bathrooms of today, which are possibly different from bathrooms of old (the Chazon Ish writes that he has a safek concerning the status of today’s bathrooms), and the more so for bathrooms that are used for other purposes as well as “using the bathroom.”
One should not speak while actually “using the bathroom.”