Student or Learner
I beg to say that I will not be able to come to the university of 9 Nov, So please grant me leave for one day .I am very thankful to you
I beg to say [regret] that I will not be able to come to the [unnecessary article] university of [on] 9 Nov [don't use abbreviations in letters], [. Use a period, not a comma, between sentences] So please grant me [i request] leave for one day .I am very thankful to you [Thank you for your consideration]
I regret that I will be unable to attend classes on November 9, because of another longstanding personal commitment that day. I request leave for that one day only. Thank you for your consideration.
Fill in the "story" with whatever excuse you feel is appropriate. (e.g., "...because of my grandmother's funeral" or whatever). I do not know if the "request leave" is an appropriate phrase in your university. I would have simply left that sentence out entirely - and simpy have announced my absence and ended with a thank you comment.