With whom did Hashem speak in a cloud?
Rashi: It was even with Shmuel - "ha'Yesh ba'Zeh ha'Ro'eh; va'Ta'anenah Osam va'Tomarnah Yesh" (Shmuel I, 9:12) - they saw a cloud tied over his doorway. This is like it says "v'Yesh Asher Yihyeh he'Anan" (Bamidbar 9:20).
Radak, Malbim: Moshe and Aharon.
Radak citing Rav Sadya Gaon: It is among matters that are a sign to a Navi, that what he sees and hears is from Hashem. Sometimes the sign is a cloud that stands in front of the Navi, and in the entire sky there is no other cloud. So happened for Moshe, Aharon and Shmuel.
About whom does it say "Shamru Edosav v'Chok Nasan Lamo"?
Radak: Moshe and Aharon guarded the Edus and Chukim that You gave to them. They guarded them to tell them to Yisrael without addition or detraction. It goes without saying that they guarded what You command them alone, e.g. to Moshe during the seven days of Milu'im, to Aharon about guarding Kehunah - "Atah u'Vanecha Itecha Tishmeru Es Kehunaschem" (Bamidbar 18:7) and Shmuel guarded His testimonies, instructed Bnei Yisrael and returned them to the good path - "va'Ya'avdu Es Hashem Levado" (Shmuel I, 7:4).
