Is it possible to update XWIKI directly from version 5.03 to 11.10?
You’ll need to read every release notes to see if there are things to do. That’s a lot.
Recommendation: always upgrade when there are new versions and don’t stay on an old one for long 
It should work but it depends a lot on the number of customizations you have made to the standard pages.
I would recommend to try the standard upgrade process before https://www.xwiki.org/xwiki/bin/view/Documentation/AdminGuide/Upgrade#HAlternativeStartfresh2CplusExportandReimportyourdata since this one usually create more problems than it solve and is to be used as last resort.