The conditions for fare class J are those at the link you included above:

For European flights:
Every J class ticket (and every C, D, I and Z ticket) is Business Class Fully Flexible; It has no minimum stay requirements; change is possible; cancellation is possible; Upgrade with miles is not possible [there is no higher cabin to upgrade into]; and FB miles are earned at the rate of 250%

For longhaul flights:
Every J class ticket is Business Class Fully Flexible; It has no minimum stay requirements; change is possible; cancellation is possible; Upgrade with miles is possible from J [if there is a higher cabin to upgrade into]; and FB miles are earned at the rate of 175%

If this is not enough information for you, what more do you want?

Like I told you above, it is the fare basis that contains the full conditions. "J" tickets are not all identical. The main things will be similar, but the fare rules attached to two different J tickets can be very different, too.

You seem to think that "J" is the last bit of information needed to identify everything about a ticket. It's not.

Let me make an analogy using the telephone system. The airline is like the country code [as I'm sure you've noticed, Lufthansa uses a different fare structure than AFKL, for instance, just like each country has its own telephone number system]. Once you've got the "country code" [aka: airline] you can then look at the "area code" [aka: fare code] of a phone number - it only gives you some information, like whether it is a mobile number, or which geographical area the phone is in. This is like the fare class. You can tell some details just from this information, but you don't have a uniquely identifying number yet. To completely identify the ticket, you need more than the area code - you also need the telephone number [aka: fare basis code].