doing a PHD and hope to find work for future

My master was about one field of computer networking (wireless sensor network). now I want to apply for PHD in US or Canada.

the problem is I want to do a research on the field that help me to find a job in future. In more than a year and half I just waist my time by trying to understand some one else codes!!! and finally all of my development or better to say my added code to him is less than 200 lines!!

So you can see there is no improvement on my programming skill. I really have a bad mood about what wrong I was done.

Why I waist my time to understand some one else code. His code was dirty!! without any documentation . and I did not have anther choice.

But I do not like to do this mistake again on my future PHD. I want to change my field to the better field but the problem is : I do not know how to know: doing which research help me to find a job in future ? Can you suggest me some ways?