Be well up in something
Definition 1 of 1
Pro Tip 1/3Deep Knowledge
Refers to having a deep and comprehensive understanding on a topic, beyond basic familiarity. 
After years of research, he is well up in renewable energy technologies.
Pro Tip 2/3Specific Context
Used when someone has expertise in a very specific field or area of study. 
The professor is well up in 18th-century French poetry.
Pro Tip 3/3Informal
This phrase is informal and more commonly used in casual or conversational contexts. 
Ask Mark about fixing cars; he's well up in auto mechanics.