The literal translation, "I know with what oxen I am plowing" ("ploughing" in the British spelling) or "I know the oxen I use for plowing", as you put it, is unusable; it sounds bizarre and no one will understand the figurative meaning. "I know my oxen" is better, but again, as you say, the point of the expression is lost. What does "knowing your oxen" mean? People will not get the point.

On the other hand, if you simply use the figurative meaning of the expression, "I know who I'm dealing with", no one will understand why the picture portrays a pair of oxen, or why such a picture has this title. The point of this Spanish title is the wordplay, and if that is lost the title becomes arbitrary.

The actual meaning of the expression, it seems to me, is less important than the fact that the title expresses the literal subject of the image and a figurative meaning simultaneously. What is needed is a title in English that does both these things: that refers to the image but is also a proverbial expression. What that expression actually means, in this case, is secondary, I think. In other words, it doesn't really matter whether the title actually means "I know who I'm dealing with".

So I would suggest some variant of the expression "Plow your own furrow" ("Plough" in British English), meaning "go your own way", "act independently". It would be nice to use an expression that mentions oxen, but I can't think of anything suitable. It could be "I plow my own furrow", "Plowing your own furrow", or whatever version seems most suitable.

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Note added at 14 hrs (2012-07-20 07:54:39 GMT)
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In the light of Silvia's comment, let me say that I am well aware that "Yo sé con qué bueyes aro" does not mean "I am plowing/ploughing my own furrow". If there were an expression in English that referred to oxen or ploughing and meant "I know who I'm dealing with", then of course we should use it, but there is no such expression. Therefore we either have to use an expression that has the same (figurative) meaning (I know who I'm dealing with) but has nothing to do with the picture, or else use an expression that does refer to the picture but means something a bit different. As I have tried to explain, I think the latter is preferable. The expression I have proposed, though different, is in the same spirit: I am aware and decisive.

This is clearly a kind of emblem picture, in which the picture illustrates the literal meaning of a figurative expression. It seems to me vital that the English title should also be of this kind: a figurative expression of which the picture serves as a literal representation; otherwise, the emblematic nature of the picture is lost. In this particular case, that requirement takes priority over rendering the precise meaning of the Spanish expression, in my opinion.