Always be positive and don't be over confident. There are various parameters to select a candidate. It also depends on how much experience you have and which company you are targeting.
- If your target company are like Amazon, Microsoft etc. They check designing skills, data structures and programming proficiency.
- If you are target any technology specific (telecom) company such as Aricent, Radisys, Qualcomm, Sasken etc their focus will be mainly on technology if you are experienced guys and if you are fresher then mainly programming (C/C++), operating system and linux OS awareness.
Since it is very general / vague question, it is difficult to cover all the aspects of interview. It is completely based on individual experience.