is it a Sunnah to cut nails on friday or thursday?

Answer

It is Mustahabb (commendable and desirable) to pair the finger nails every
Friday. Only a Mujahid is exempted from this and it is preferrable that he
lenghtens his nails because it can be used as a weapon to attack the enemy.
It was aso the blessed habit of Nabi alaihis salaam that he would pair his
nails and not let them grow long. It is also noted in the books on
Jurisprudence that he who lengthens his nails, his sustenance and income
becomes straitened and restricted. (Shaami vol. 6 pg. 405, H.M. Saeed).

Also, one should remember that at the time of wudhu it is necessary for the
validity of the wudhu that water reaches below the nails if the nails are
longer than normal. Many a times women are busy in their choirs of the
kitchen wherein different types of ingredients tend to stick under the nails
and if not removed, Wudhu will be invalid if it does reach the bottom of the
nails. Therefore it will not be permissible to keep long nails
unnecessarily.

and Allah Ta’ala Knows Best

Mufti Ebrahim Desai

Source