4-4 point low approach two-space low pincer
The pincer and the common replies
This is a special-purpose pincer and is not ordinarily found in modern professional play[1]. See below.
White's ordinary answers are at a, b and c. The jump out at j, standard in old Chinese games, is sometimes seen.
Joseki references
Suzuki and Kitani's Small Joseki Dictionary also state that the two space low pincer is rare. (And that's historically.) However, they give this diagram as joseki, with the comment that you can't say that this is better than having a three space low pincer.
The fact that it is still rare does not mean that expert opinion about it has been revised.
They also say that in response to the double kakari produces a somewhat favorable result for Black.
This was at a time when the usual advice was to attach to the stronger stone, suggesting a play at a instead. Today pro opinion about that advice has changed.
A possible theory
Here is a possible theory as to why it is not common, but keep in mind expert advice on the matter is not final.
Consider what happens after White jumps into the corner and the usual follow-ups are played. If now Black played at a, the pincer would feel overconcentrated. On the other hand if he omits a, White jumps out to and the pincer feels slack. Hence it is difficult to find a balanced follow-up for this pincer, locally. This is why the marked stone needs extra purpose in relation to the upper right corner.
[1] This may not be true any more. See 11thNongshimCup/Stage 1 Game 1 for an example. The continuation in that game is:
Note that black has an enclosure to the right of this diagram in the game.
tapir: today, a dan player in our local club asked about the two-space low pincer why it is fashionable again. the argument that after the jump out the shoulder hit isn't as nice anymore seem to have impressed him a little bit. (the same explanation i offered at the nongshim cup game) i wonder whether some stronger player can offer his/her opinion.