I too had the same doubt... but when I googled.. I found that new version of OOXML files do not require dom4 files.
Refer URL: https://poi.apache.org/overview.html
Also i have attached the screenshot.
Yet, I would let trainer have a final say on this
what is the solution to get dom4j file?. from the url >http://www.java2s.com/Code/Jar/d/Downloaddom4jjar.htm
do we need it if we have the latest POI apach zip file?
thanks