Huh, that's interesting. There should be a "subdue" command but there isn't.
Non-lethal in D&D/PF leads to unconsciousness. Non-lethal in animal play is just the human equivalent of wrestling.
1. If the animal companion already knows Trip or Grapple as special attacks, you could just use those as part of an Attack command, depending on the GM.
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2. If you have the animal has the Attack trick, but not the Trip or Grapple, you can teach it the Maneuver trick (to get trip/grapple/etc.).
Maneuver (DC 20): The animal is trained to use a specific combat maneuver on command. An animal must know the attack trick before it can be taught the maneuver trick, and it only performs maneuvers against targets it would normally attack. This trick can be taught to an animal multiple times. Each time it is taught, the animal can be commanded to use a different combat maneuver.
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3. Here is a good page on Animal Companions and their Tricks, in the rules heavy area known as PFS:
http://paizo.com/paizo/blog/v5748dyo5lejb?Animals-and-Their-Tricks
Most relevant section:
"A trick it does not know is a full-round action at DC 25. There are, however, a few ways to make this easier.
Druids and other classes with the animal companion feature get a +4 circumstance bonus when handling their own companion from the Link class feature. This also allows them to handle an animal as a free action, or use a move action to push the animal."
So, this would seem that you could do a DC 25 check and a move action to get the companion to do what you want.
Later, it also says:
"So how do we reliably overcome DCs like 25 at reasonable levels? I think Skill Focus (Handle Animal) is certainly an option for some druids who see themselves as dedicated animal companion users. There is also the training harness item from page 76 of the Advanced Race Guide that will give you another +2 bonus on these checks. The most important thing is to not dump Charisma."