"Who plays soccer the best?"
I agree, this sentence structure is very difficult, the literal translation reads, "Who+play soccer+ play+ 得 ('de', particle)+ the best (最好, zuì hǎo)? 谁+踢足球+踢+得(de)+最好(zuì hǎo)? For me, the question's structure has several interesting features worth noting which might help others to help understand the complex grammar rules: (Note #1) 最好 (zuì hǎo) is an 'adjective' that means 'the best'. (Note #2) 得 (de), is a 'particle' used here to show 'degree complements'[- a 'complement' is something that appears right after the verb and adds more information about it.] I think that the question's structure, is, Subject 谁+Verb 踢足球 + Another Verb 踢+ Degree Compliment 得最好? These websites are useful to read, https://www.chineseboost.com/grammar/de-grammar-summary/, https://resources.allsetlearning.com/chinese/grammar/Degree_complement#Degree_Complements_with_Objects