That depends on why you’re looking for them. 
The actual real Standard Rules themselves can be read by going to File → Open Extension → Graham Nelson → Standard Rules. But they’re not really documented and can be hard to read through unless you already know what you’re looking for. They also only tell half the story, as a great deal of things are implemented in the I6 code instead, which is less easily readable (though you can still find it if you go looking).
You might want to have a read through of the annotated rules; this is quite old (I’m not sure if there’s a newer version around somewhere) and many things have changed since then, but a lot of it does still apply, so this may help, especially if you compare the rules here with the real Standard Rules.
Having said all this, for most purposes a combination of looking in the Documentation and looking in the Index (especially the latter) gets you a long long way, without needing to look too closely at the Standard Rules themselves.
For example, clicking through Index → Actions → Taking shows you all of the Check rules controlling that action. While this doesn’t tell you the precise conditions it checks, usually this is fairly apparent from the names of the rules, and if not, once you know the name of the rule you can more easily locate it within the Standard Rules themselves. Better still, the Index automatically updates with any extensions you’ve included as well as rules from your own story.
To find that particular rule mentioned above, though, you need to look at the Rules tab instead, under the deciding whether all includes activity. Using the RULES debugging verb is another way to help locate which rules are affecting things in play.