It depends on WHO it is and the conjugation. I WANT You WANT He/She/It WANTS We WANT They WANT

In the present indefinite tense, we put s/es/ies after the main verb if the main subject is singular. STATEMENT-- I'm Li Fengyang, a Chinese guy "who wants/want to master English". In this above statement the main subject is "who" which is an indicator for "Li Fengyang" and "Li Fengyang" is obviously singular therefore WHO WANTS TO MASTER ENGLISH is correct. Another example-- They are MIKE and LITA "who want to master English". In the above example we have used "want" because the main subject (in present indefinite tense part) is plural (MIKE and LITA).

wants

Yes, definitely 'a guy who wants.'

I am Li Fengyang. I am a Chinese guy. This Chinese guy wantS to learn English.