What should I expect for an unannounced GA visit for touch-n-gos at San Jose? I understand that KSJC is a busy airport. I have done touch'n'gos at Oakland (also a busy Class C airport), but they have three dedicated runways for GA aircraft. 

There is nothing about which runway is preferred for GA operations at SJC in the Airport Facility Directory notes.

What should I expect if planning an unannounced trip to SJC (arriving from the north/north-east)? Are touch-n-goes tolerated (i.e. staying in the pattern)? Which runway should I expect to be directed to? Is there anything else I should know?

I'm looking for local knowledge from someone with experience flying in the area, for example "GA operations are usually conducted on 30L, as the air carrier terminal is on the the other runway, and transient parking is adjacent to this runway" [I'm not sure this is the case, this is just an example of the type of information I'm looking for].
I have flown several times to SJC for touch and goes. I have always been on the weekends, and probably in the afternoons. It is a lot of fun, especially because the runways are so long for a small plane. I think I’ve been three times, and each time they have accommodated me on 30L. The wind is almost always favoring the 30 runways, and I don’t remember ever being cleared for 30R.

They will occasionally make you circle briefly before entering the C. They will also sometimes make you extend for a pretty long pattern to the SE if they have a big fella cleared for 30R. All the big commercial jets seem to be sent to 30R, and it is small GA jets that use 30L.

I have only done touch and goes, as I wanted to get out of the way quickly. But I get the impression that the tower is happy to accommodate as long as they’re not too busy. My instructor told me that they sometimes will say ‘no’ if they are busy, especially during the morning push, but I have no experience of that.

Have fun! There’s a beautiful 787 that is often at the terminal, keep an eye out for it!