I don’t think there are single entity that obviously benefits. Russia, Ukraine, the EU and multiple outside actors have reasons to attack the N1 pipeline. The slightly less obvious secondary effect is a push to open the N2 pipeline but that’s just a start.

Beyond state level actors you need to consider everything from Russia’s Gasprom having pending lawsuits this helps with to 3rd party gas suppliers benefiting from increasing sales at extreme gas prices. Stock speculators could be located anywhere and benefit from knowing about such attacks ahead of time. Even something as odd as a fringe environmental group could be behind it.

At best depending on how difficult such an attack is you can somewhat narrow things down.