QuestionCan you breed a male African Side Neck turtle with a female Red Ear Slider turtle?
AnswerProbably not.
The most primitive kinds of turtles are those that wrap their heads around under the shells- the Sub-Order called "Pleurodura", or 'side-neck turtles'. These include the Mata-mata, all side-neck turtles, most Australian turtles, snake-necks, etc. The African Snake Necks belong here.
More modern turtles pull their necks in with a vertical S curve, the Sub-Order "Cryptodura" or 'hidden neck turtles'.
The two groups separated so many millenia ago that they do not share enough DNA to successfully breed, although they may mate once in a while, and may even lay eggs- they would almost certainly be infertile.