what is the differences between these two sentences? who I am. who am I .
It depends on what comes before the structure.
If you are using this structure [WHO I AM] in isolation you would say: Who am I?
If you add an introductory sentence before it, then it is the other way round. I mean:
Do you know who I am?(The introductory sentence is 'Do you know...'
Whenever you place some introduction before WHO I AM you need to change it!
What time is it?
Do you know what time it is?
Hope this helps!
P.S: What you are asking has to do with the 'DIRECT vs INDIRECT QUESTIONS GRAMMAR'. Just google it for more information :D
What are Indirect Questions?
The rules are different for indirect questions! Direct questions are the “normal” questions that we can ask to friends, family members, and people who we know well. You can form direct questions using the QUASM model that we learned last lesson. Example of a direct question: “Where’s the bathroom?” Indirect questions are a little more formal and polite. We use them when talking to a person we don’t know very well, or in professional situations, and their form is a little different. Example of an indirect question: “Could you tell me where the bathroom is?” - See more at: http://www.espressoenglish.net/direct-and-indirect-questions-in-english/#sthash.UNML1cBB.dpuf