I didn't get my doctorate in KM, but I did write my doctoral study about KM in support of earning my DBA, as opposed to a PhD, in Project Management. While there are great ideas for topics from our colleagues, I found it was best for me to research something I could enjoy through the years of writing my study as well as the work after I earned my doctorate. When I first started writing and researching, I wasn't 100% sure about what to write and my Chair gave me some really good guidance along the way. Think about what you would like to be doing if you weren't in school and that should tell you what your interests are and then make your research support your future. Once you earn your doctorate, that research can support your follow on work since that will be something you need to have in your study anyway. If not, you'll just have a great piece of really expensive paper.