Is it permissible for a person who has to make up for missed fasts to fast six days of Shawwal (the month directly after Ramadan) before making up for the missed fasts?
Yes, it is permissible for him/her to do so, but it is better that they make up for missed fasts first. And Allah Knows Best.
What is the best remedy for a person who experiences Waswasah (whispers of the devil) during Salah (prayer)?
Such a person should ignore the devil`s whispers, contemplate the Quranic chapters and verses that he/she recites, look directly at the place of Sujood (prostration), make supplication to Allah, and take refuge in Him from the cursed devil.
What is the Time for Making up Fajr Prayer and Other Missed Ones?
All perfect praise be to Allah The Lord of The Worlds and may His Peace and Blessings be upon our Prophet Muhammad and upon all of his familty and companion.
The Messenger of Allah (PBUH) said: "Whoever forgets a prayer, let him perform it when he remembers it." [Muslim]. As soon as you (Questioner) wake up, you are obliged to make up the missed Fajr prayer. And Allah Knows Best.
Does the clipping of nails nullify ablution?
No, it does not, and it is preferable to wash the hands afterwards.