Question

write application to your principal asking for 2 days leave

Answer 1

To,
The Principal
(School Name)
Sub:Leave for two days
Through:The class teacher(in most cases)

Respected sir,
Most humbly and respectfully,I beg to state that I am not feeling well since last night so,I went to doctor and he told me to take rest for 2days.So I will not be able to attend the school on next 2 days.
I will be grateful to you for this.

Your obedient student
(Name of student)
(Class and division)
(Date)

Hope this helps

Answer 2

(If this leave letter is written by the parents, Here it's from the father)...

From:
(Your father's name)
(address
------------
------------)

18th April 2018

To:
The principal,
(Your school name)
(School's address
----------------------
----------------------)

Respected Sir  / Madam,

     Subject : Regarding leave for two days.

     I am xxx (the father's name), father of xxx ( your name), studying in (standard and section). As my family is going for a function (just an example), my son/ daughter wouldn't be available for two days. I kindly request you to give two days leave for my son/daughter.

Yours faithfully, 
(Father's sign)
(Father's name).