How to get those professional looking peaks on top of tiramisu? Most tiramisu-recipes end with the last layer of mascarpone mixture spread on the last layer of lady fingers/sponge cake (and some chocolate powder on top). So you have a flat surface.
I've seen pictures of tiramisu with a bumpy surface, like small peaks (picture of what I mean).

I want to replicate the peaks, but I'm not sure how to do this.
I already tried to form them when the last layer of mascarpone mixture was on top, but this didn't turn out well.
My next attempt will be with a piping bag. And the one after that will be with cold mascarpone mixture, so it's a bit more firm.

However, I'm not sure any of those will work, so in advance of making two batches of tiramisu, I'm asking if anyone knows how to form the peaks, or if anyone knows that my two next attempts will fail.

I've seen also this question, but I don't think that would help me. If you think otherwise, please say so.
You probably wont be able to get that exact result with a pastry bag because the almost perfect square grid they are divided into. I still think a pastry bag will be your best bet.

I am not sure were you got that picture but my guess is that the tiramisu was machine made and the marks and peaks are from the tooling that was made for the machine to deliver the mascarpone topping.

I would try a good sized round tip on a pastry bag and make my dot and slowly raise up and cut it off by stopping the pressure on the bag and pulling straight up.  It has worked for me in the past.

My background is not in pastry though so you may also just go to a local bakery or wedding cake designer and ask how they would do it.  They will probably tell you.