I lived in SJ for awhile but don't now so can't be that specific on what trails are open for bikes etc. but have your friend check out Almaden Quicksilver Park it's out at the south end of Almaden Expressway...I think it has a website for more exact directions. Also not far from there is Santa Teresa Hills... not far from the junction of Hiway 101 and Hiway 85...this may be also on the site for quicksilver. Those are a couple in San Jose but some of the other suggestions such as Page Mill and up around Palo Alto are probably nicer in part because you're out of the pit they call the Santa Clara Valley.
There's a few ok bike paths in SJ too though, ones that are not along the road but dedicated just for bikes, (and runners etc too) One runs from Campbell and then through Los Gatos and on to Lexington Resevoir and another is over near 101 and runs along Coyote Creek...I think it goes all the way down to Morgan Hill or maybe even Gilroy. 9These last 2 aren't trails but as I mentioned bike paths.)