"Who wants to continue to go to school in Japan?"
Translation:Siapa yang mau melanjutkan sekolah di Jepang?
You can leave it out in spoken Indo, but it is better to learn by keeping it in ... better grammar and in different contexts it would be needed. I find it helpful to think in terms of ... who is the one / who is it that ... If I can write the sentence in these ways, then using 'yang' would be an option.