In his thesis, Jacob Lurie mentioned two work in preparation (by him), namely "Virtual fundamental classes and the motivic sphere" and "Geometric derived stacks". Now that much is written in the DAG series and the two books (Higher Algebra and Higher Topoi), I'm wondering if anybody here know if these two papers are contained in the DAG series already or still yet to be written?

I'm not sure I understand the question (unless it's intended as general curiosity about the progress of Lurie's work). I can see two legitimate options:
Of course if you're just starting to think about a problem it might be wiser to find your own questions rather than trying to prove something you saw announced in Jacob's thesis.. 


In December 2005, Jacob Lurie visited Berkeley, and I asked him about the main results of the motivic sphere paper (N.B., his dissertation was from 2004). He replied, "I cited it, but it does not exist." It is possible that he wasn't completely serious. 


Lurie repeatedly cited "Virtual fundamental classes" for seemingly unrelated topics. I don't believe that he has yet returned to any of those topics. He cited "Geometric derived stacks" fewer times and more vaguely, so it is harder to track what happened. I think some of the material appeared in "DAG VIII: QuasiCoherent Sheaves and Tannaka Duality Theorems," which got folded into the second book. I think he changed his plan and spread out that material, while the first paper has remained intact and just hasn't appeared yet. 


It's worth noting that Lurie's thesis is not on his webpage, and is not regularly updated like the papers which are on is webpage. I would take this to mean that you're supposed to be reading the current versions of this material in the DAG series, and not reading the 8 year old outline. 

