He wasn't referring to any specific attacks, but they happen all the time now due to all of the violent refugees. Sweden is now the grenade capital and rape capital of Europe because of how many refugees it has taken in. Also, here are a couple things that happened on the night that the President mentioned. I'm sure more happened though, especially in the Swedish city of Malmö.

FAKE NEWS. http://imgur.com/a/Jf4uo

Many Swedes, on the other subreddit

R/Sweden consistently debunks your propaganda. Go on there and look for yourself. Or maybe they don't in alternative fact la la land

There is no supranational conspiracy. You've spent your time reading far-right propaganda.

The entire migrant rape myth was debunked by a rightwing Christian university - BYU https://eucenter.scrippscollege.edu/wp-content/uploads/files/2016/03/Davis-and-Vidler-Paper.pdf

This article details a very good reason why you can't compare countries' crime rates http://www.bbc.com/news/magazine-19592372 https://www.reddit.com/r/europe/comments/36d3z8/is_sweden_now_the_rape_capital_of_the_world_no/

As with any rightwing astroturf movement, it's extremely important to follow the money. This article does a good job of delineating who the players are in the rightwing muslim hysteria movement. Very well sourced.

https://www.thenation.com/article/sugar-mama-anti-muslim-hate/

The one thing you are correct on is Sweden has higher numbers than any other country but that was already the case due to their very liberal reporting practices i.e. a good thing Swedish law uses ‘extensive counting’ when reporting rape and as such counts every instance of rape separately, even if committed by the same accused on the same day (Amnesty International, 2010), arguably producing higher figure than countries using less extensive reporting criteria.

http://www.theglobeandmail.com/opinion/swedens-rape-crisis-isnt-what-it-seems/article30019623/

Again I doubt actual facts not cherrypicked propaganda will convince you.