We japanese don`t say "gakkousei". Gakusei = Gaku(学問=study) + Sei(生徒=student) = one who study

Gakusei がくせい Never heard "gakkousei".

You can pronounce "Gakusei" as is. We also use the word 学生 for the university or college students, which is not Gakkou, but is called Daigaku or Tandai. So it is never Gakkou + Seito, and Gakusei, which is Gaku(Studying) + Sei(Student), is pronounced "Gakusei" as well.

i meant if it's gakusei , do we pronounce it GaKKousei ? with 2 KK