no matter what 只能引导让步状语从句不可以引导名词性从句.如：No matter when I'm unhappy,it is my friend who cheers me up .不管什么时候我不开心了,总是我的朋友使我振奋起来.
whatever既可以引导让步状语从句,也可以引导名词性从句.如如：Whatever was said here must be kept secret.我们在这儿说的无论什么都必须保密.（名词性从句 ）如：The lawyer seldom wears anything other than a suit ,whatever the season is.无论什么季节,这位律师除了一套西装以外很少穿其他衣服.（让步状语从句）
whatever在句子中做宾语,如whatever you want,无论你想要什么 .
however在句子中做状语,如 however you want it,无论如何你想要它.
前者的句子必缺少成分,you want句子不完整,缺宾语.
而后者用的句子是完整的,you want it,这句话是完整的.
所以,判断是whatever还是however,只要判断句子完整与否就好了.