If you are using Picrust within Galaxy with the pre-computed reference COG files, this is the source most use (from the Tool Shed's web page for the tool - drill down into "Valid Tools" to view in full):
Precalculated files: ftp://ftp.microbio.me/pub/picrust-references/picrust-1.0.0/
Some other useful info is in this Q&A post at the tool's google group: https://groups.google.com/forum/#!topic/picrust-users/bJMbEFD2OUU
To be absolutely certain about the KEGG version in use at any particular public server, contact the administrators and they can clarify.
Hope this helps! Jen, Galaxy team