Hi all, I am bit newbee to this business. I am trying to record my guitar and some vocal by Sonar HS6. As an external soundcard I have Focusrite Scarlett 2i2. I am facing two problems: 1. I am not hearing anything through the headphone I have plugged into my laptop while recording or playback. I thought I fixed the issue when I selected only speaker as my audio output device, but the audio engine crashed after a while. 2. The guitar I am recoding is getting recorded as a mono track. I want a stereo track for that. Does anybody have a fix for these issues?

Welcome to the forum!

Well, those are actually not issues :o)
1) You should plug your headphones in the Focusrite, not the PC.
2) Check that Focusrite is selected as both Playback and Recording timing master in Options-dialogue. Also make sure you are using ASIO drivers (or alternatively WDM), and have them selected as input/output drivers. See that your integrated soundchip is NOT selected anywhere in SONARs settings.
3) Mono source, like guitars, vocals etc.  should be recorded as mono. There's no use recording mono source in stereo, as then you can not pan it in case you want to position it in the stereo field. Stereo recording, obviously, requires two inputs, left and right, which you can not get from a guitar. If you want a spread sound for guitar, you need to either double track the part, or copy the track, then move one of the clips 10-30 ms apart, and pan them to your liking.
4) To hear what you are recording, the effects in the FX bin and all, you must enable "Input echo".