For example, every employee need to "discuss" or "confer" or "consult" with your boss for vacation time. What is difference among them? In this case, which ones are correct and which is most appropriate?
Discuss and confer are synonyms. When you say, "Every employee needs to discuss/confer with his boss.", you mean that every employee must make sure that he talks about the concerned topic to his boss.
When you say, "Every employee must consult his boss regarding vacation plans.", you mean that every employee must seek information or advice regarding the concerned topic, from his boss. Here, consult nearly means meet for a purpose.
Discussions/conferences are group activities. Everyone gets a chance to contribute to the discussion.
A consultation is mostly one-sided. One person offers advice and the other listens to it.
In this particular context, discuss, confer and consult have almost the same implication. You can use any one of these. If you want to be specific, check their meanings and choose the most appropriate one.
Note the succeeding preposition: 'Discuss/confer with' and 'Consult (no preposition)'