这三个词差不多，怀疑含有贬义，质疑是中性词，而置疑多用于成语：不容置疑。 Three words are similar. 怀疑 is a derogatory term, while 质疑 with barely personal feeling. 置疑 is rarely to see, except 成语：不容置疑。 I hope it is helpful.

怀疑 质疑 置疑 怀疑，相当于suspect doubt; 置疑 质疑 两个词有包含关系。 首先，质（有‘提出’的意思）顾名思义 质疑 即 提出疑问； 而“置疑”含有“质疑”的意思，但置疑通常用于否定情况 如：不容置疑。

1.怀疑means suspect I suspect/doubt he is a thelf. 2.质疑 for example the authorities or experts who are skilled in certain field. and they put forward a theory. but you dont agree with it or you dont think it works. and you say does it really work? it is you 质疑 them, which is a formal way. 3. 置疑 is rarely to see. it is more common used in an chinese idiom（成语）---不容置疑。this plan is 不容置疑 means this plan is precise.