welcome to our community, it’s lovely to have you here.
As @alexesc mentions, it’s definitely possible to connect both Processing and Sonic Pi and the most obvious route is to send OSC messages between them.
I’m not an expert in Processing itself (although I have used the underlying technology so have some understanding of what it can do - just not any experience with its syntax). However, there might be some people on here that do have knowledge and could help out.
However, I think your question may be a bit too broad - it’s hard to know how to offer advice without knowing what your aims are in a bit more detail than connecting two bits of software together. Do you have any idea what you’re trying to do? What would be the simple first step towards your aims? Trying to break things into little, clearly communicable aims would definitely help us help you here.
As a first step I’d definitely take a look at the OSC tutorial sections for Sonic Pi here: https://sonic-pi.net/tutorial#section-12
That might help you think about whether you’d like information from Sonic Pi to be sent to Processing or whether you’d like information from Processing to be sent to Sonic Pi or both!
A quick google for OSC and Processing brought up this page which suggests using the OSCP5 library which is probably where I’d start on the Processing side.
Still, it would probably help a lot if you can let us know what you have in mind - both in terms of broad ambition and in terms of a simple first step.