How to make this sound:

Video Text:

Ch and jj are paired together because they take the same mouth position.  Ch is unvoiced, you use only air to make the sound, and jj is voiced, you produce the sound with the vocal cords.  The position:  the tongue comes up and presses the inside of the top teeth, here.  Ch, ch.  The tip of the tongue touches the roof of the mouth, close to where the mouth joins with the front teeth, but it's not touching the front teeth.  Ch.  The sound is made when the tongue pulls back from the roof of the mouth.  Ch, ch.  The teeth, as you can see, come close to together, ch, the do come together.  And the lips come in just a little bit, which means that they also go out just a little bit.  Sample words:  chump, jump ... chess, Jess ... chalk, jot ... chump, jump ... chess, Jess ... chalk, jot.

International Phonetic Alphabet symbols:  [], []

As you can see, the IPA uses two symbols to represent each one of these sounds.  For more information, and to see these sounds' occurrences in other languages, see Wikipedias pages (voiced, unvoiced).