Presentation - How to make a Tiramisu to be photogenic?

Mind what you cut the tiramisu with - your knife might not be sharp enough, or even too sharp, or of the wrong kind, or using the wrong kind of technique (pull vs push vs rock cut give different results here).

Exactly the same, of course, applies to the camera equipment used.

But what matters most is how to light the texture of the cut - light it head on and in a nearly collinear to the camera fashion and you will suppress a lot of the texture since highs and lows will be equally lit. Light it from the side and you will emphasize the texture. A combination of both will probably work best. Mind what shadows (of the whole piece of tiramisu) you will cast, and also consider these shadows in the plating and background you use. Mind that white plates can act as a reflector lighting textural features from below (which might be desired or undesired) - but be aware that unwanted hard shadows (moreso if they pick up a color cast) on white backgrounds can be easily overlooked when framing the picture but can look atrocious in the final result. Consider polarizing filters or even using cross polarized lighting if reflections from shiny crockery or shiny, glazed parts of the dessert give you problems.

One thing you could try is heating the knife. Use a sharp, smooth-edged knife and heat it in hot or boiling water just before cutting the tiramisu. Freezing the tiramisu beforehand may also help. But you won't know what effect it will have on your particular creation until you try. Perhaps the one in the other photo has thinner pastry layers, which would give more resistance to cutting.