A Tokubetsu Jonin is simply a Chunin with a Jonin level skill in a certain area. So for the most part, they are still equal to Chunin in most ways. However, there are certain areas, i.e. teaching, bodyguarding, assassination that they perform even better than full Jonin. Tokubetsu Jonin is a separate rank, walking in between the Chunin and Jonin. If the Tokubetsu Jonin were to balance their skills in other areas, they would be promoted to a full Jonin.
Ebisu is a good example of a Tokubetsu Jonin. As a Tokubetsu Jonin, he specializes in teaching. As such, he tutors some of the brightest young shinobi in the village, especially those of very important shinobi. For example, Konohamaru Sarutobi, the grandson of the Third Hokage.
Now, Ebisu is treated as an equal by most Chunin, and he still shows respect to higher Jonin like Kakashi. However, even Kakashi, one of the strongest, most elite Jonin, had great respect for Ebisu’s teaching abilities, as they were much greater than his were.
Ranks work very specifically in Naruto. Academy Students are inducted to the Academy just as long as they have the physical and mental capabilities to learn. However, that doesn’t guarantee they will graduate. In order to graduate they have to prove capable of the next level, Genin. Genin rank is determined by a focus on the basic E-Rank ninjutsu, and other mental and team building exercises. They are then tested by their potential Jonin instructor, to see if they are really capable. Naruto’s class, for example, of all the students that passed the exam and graduated, only 9 actually achieved Genin rank.
The Chunin rank is even more difficult, because it involves the very difficult Chunin Exam. Although the exams very from time to time, the mostly test mental and information gathering skills, teamwork and cooperation, and most of all, your overall skills and abilities as a shinobi. Luck is also a big factor, as sometime you get matched against someone you can’t beat, and you don’t get the chance to prove yourself capable. Even shinobi who are Chunin-level somtimes need to take the Chunin Exam multiple times to properly pass, as it is usually only the few strongest who make it to the Third Exam each time.
Now, this is where your question comes in. All Jonin, Tokubetsu Jonin, and Chunin have passed the Chunin Exam. So there is a minimum level of skill to each, in that they all have those lessons down, and have a certain level of power.
Chunin are at that level. However, if they want to be Jonin, they need to gain more experience and raise their skill set to an even higher level. That level is determined by the Kage.
However, not everyone grows their skills equally, some shinobi are just more capable in certain areas. These are the Tokubetsu Jonin. As opposed to Chunin who are growing their overall skill set to Jonin, a Tokubetsu Jonin’s specialized skill allows them for additional responsibity as they develop their other skills more to develop into Jonin.
What’s more, not evey Chunin or Tokubetsu Jonin reaches Jonin, in fact, Jonin is a very elite, rare rank. However, they are not as rare as the Kage rank. As a result, most Tokubetsu Jonin will often just specialize in their skill until they retire. Basically becoming a master of their craft.
As the answer said above, you can have Tokubetsu Jonin who have a skill most developed than a Jonin, but without that more developed overall skill set, they wouldn’t be made a Jonin.