The Prophet used to wear lungi on the lower part of his body. In some traditions it is mentioned that he bought pyjama while according to some he wore it too. His cloth on his lower part used to reach up to shank in length. The lungi and pyjama can be worn up to ankles; it is haram to let it down the ankles.
It is not necessary to cover the topi (cap) under the amamah (turban), wearing amamah is alright whether the topi is seen or not.
Allah (Subhana Wa Ta’ala) knows Best
Darul Uloom Deoband