There are a number of things that may have been called "Direct Positive developer." The most likely are the developers used for reversal processing of black and white film. Kodak once made a film called "Direct Positive" in 35 mm and 828 sizes. It produced black and white slides when reversal processed in a kit Kodak sold. The developer in that kit was D-88:
Kodak D-88 developer for reversal processing
Water (52C) 750 ml
Sodium sulfite (anh) 45 g
Hydroquinone 22.5 g
Boric acid (xtal) 5.5 g
Potassium bromide 2.5 g
Sodium hydroxide 22.5 g
WTM 1 l
Use full strength. Develop Direct Positive Paper 45 seconds at 20C, rinse, bleach for 30 seconds in R-9, rinse, clear in CB-1, rinse, re-expose, redevlop in T-19 or D-88, wash, and dry.
This developer was used for both Direct Positive film and the corresponding Direct Positive paper, which was frequently used as the "film" in photo booths.
Later, after Direct Positive film was discontinued, Kodak manufactured a reversal processing kit that would make slides from TMax 100 film by reversal processing. I'm not sure what developer they used in the kit, but a separate instruction sheet told the photographer to use D-94, the black and white reversal first developer used for motion pictures:
Kodak D-94 reversal film first developer
Water (50C) 750 ml
Metol 600 mg
Sodium sulfite (anh) 50 g
Hydroquinone 20 g
Potassium bromide 8 g
or
Sodium bromide 7 g
Sodium thiocyanate (51%) 9.1 ml
Sodium hydroxide 20 g
WTM 1 l
pH at 27C = 12.75
Specific gravity at 27C = 1.074
Develop motion picture reversal film for 2 minutes at 20C or 40 seconds at 35C.
I don't remember if either kit used a special second developer, but the normal motion picture reversal processing instructions call for D-95 as the second developer:
Kodak D-95 reversal film second developer
Water (50C) 750 ml
Metol 1 g
Sodium sulfite (anh) 50 g
Hydroquinone 20 g
Potassium bromide 5 g
or
Sodium bromide 4.5 g
Potassium iodide 250 mg
Sodium hydroxide 15 g
WTM 1 l
pH at 27C = 12.15
Specific gravity at 27C = 1.065
After an 800 footcandle second reexposure, develop reversal film for 50 seconds st 20C or 20 seconds at 35C.