G. Mark’s Answer
It depends quite a bit on your background in Software Engineering. If your background is, say, a BS or MS in Computer Science or Computer Engineering, you're likely to have a good mathematics background. You'll want to be familiar with multivariate calculus, discrete mathematics, and statistics. If you don't remember much, you'll want to refresh yourself. You'll spend a lot of time analyzing data to be able to predict outcomes from statistical methods. Some good languages to get familiar with are R and Python. Much of this training is available for free on the web. Then look into Hadoop and Splunk, for example.
The biggie in Data Science today is AI, or more specifically Machine Learning and Deep Learning. Get familiar with ML if you're not already. Use your tutorial projects to get familiar with the practical aspects and to generate some examples to show prospective employers. You'll certainly want to be familiar with SQL and any of the SQL application environments. All this will be useful in anything computer-related anyway, as SQL is everywhere and ML is the current trend. It will eventually be necessary for just about anyone who wants to be on the forefront of what businesses will be focusing on. The nice thing is that if you have a CS degree already, you're likely familiar with much of these, and the rest can actually be learned for free on the web.
Look at case studies on-line, particularly things like Natural Language Processing and Machine Vision. Find out what the big companies are using DS for. Finally, as a DS, you'll be thrown a wide range of problems that will require your own creative approaches. If you're really a CS "code head", this is probably something you're already enjoying.