6DJ8 is the American designation, IIRC. E88cc and 6922 are european designation for upgraded "military" versions. They're all the same tube, just the gold pins and the CC at the end mean the better quality version. They're a medium mu dual triode, like a 12AT7 but with a different pinout. They're used in a lot of audiophile gear including tube mics. Worth depends a lot on whether it's truly NOS or gently used or on its last legs and you're not going to be able to tell that yourself. Value could be anywhere from $30 (used) to $60 (almost new) to $150 or more (unused and great sounding).
That is a Mullard E88CC, or known as 6922 anywhere outside of Britan. It is a Military spec 6DJ8/ECC88, and is commonly used in HiFi sound systems, but aren't often used in guitar amps. They're a dual triode, much like your other typical preamp tubes, but that's about the end of the similarities. IIRC, they have an upper voltage limit of 150V, and have a gain factor of 20. They also have a slightly different pin out than your typical 12A*7 tubes. Because of the lower voltage limits and the low gain of these tubes, they're quite difficult to adapt to guitar amp use. HiFi guys love 'em though.