best recomendation to play at 1440p at 144hz
The best cpu for gaming is still 9900k and 9700k.
But it mostly depends on your budget.
In theory the resolution you play at does not affect the Maximum frame rate you can get. The maximum frame rate will be CPU dependent. This will be independent of resolution, be it 720p, 1080p, 1440p, 4K and so on.
Actual fps will depend also on the game, assuming you have chosen a GPU known to perform well at your resolution.
Getting 144fps will depend on the Game/Title in question because:
The graphical details and calculations involved may prohibit current gen GPU's from not bottlenecking a fast CPU at 1440p. GPU's output the graphics at a particular resolution on the screen, if the GPU cannot put a picture up once every 7ms you will not get 144fps.
Most titles do not scale linearly with threads / cores so games with extremely poor optimization will not run at 144fps irrespective of what CPU you throw in there. While CPU choice does matter there is no guarantee you will get 144fps. Bottom line 144fps is not achievable for some games with current cpu's.
We can generalize however thanks to the hard work of the community that tests CPU's.
Generally speaking regarding results for high fps gaming, from a variety of benchmarks and tests, your best CPU choices right now appear to be (ignoring specialized CPU's that also perform well for gaming like Intel's HEDT with an overclock):
i7 - 9700K
i9 - 9900K (or current variants, KS and so on)
i7 - 8700K / 8086K (Believe it or not performs great with a good overclock)
Ryzen 9 3900X (trades blows at the top with i9 and i7's)
Ryzen 7 3800X, Ryzen 7 3700X (again, trades blows at the top with i9 and i7's)
Ryzen 5 3600 or 3600X (do not look down at these chips they are barely slower than a 3700/3800X for the majority of gaming titles)
i5 -8600K/9600K (Like Ryzen 5, for vast majority of titles this CPU is fast, blazing fast with an overclock....)
My recommendation => Ryzen 9 3900X if budget is not limited. While the i9-9900K is slightly faster once you overclock it the Ryzen 9 is on a superior chipset. Better motherboards, better hardware, faster PCIe, lots of advantages including really really nice stock coolers.
You will not find many haters of the AMD Wraith Prism Cooler. Intel Z390 boards are becoming scarce or overpriced. But you cannot ignore the Intel i9-9900K or i7-9700K. For gaming alone, with a board that supports high overclocking, and a good performing custom cooling loop, the fastest chips for gaming are still Intel. For the enthusiast, they are fun chips to play with. For the rest of folks, spending $1000 on a custom loop and then hours tweaking settings, not worth the time or effort. If sticking on stock settings, the Ryzen 7's and 9's hold better parity with Intel, win some lose some. Given the choice between two closely performing chips, get the chip that comes with the Wraith Prism Cooler.
If on a more streamlined budget, the Ryzen 7 3700X is the next best bet balancing cost, performance, and features.
and what gpu its good to coombine with the Ryzen 9 3900x
At 1440p 144Hz I would say RTX 2080 Super would be a good choice. Depends on games though, some will run at 144fps with far lesser hardware, some require far greater GPU or CPU or both to run 144fps. Example, Assassin's Creed Odyssey no way will you get 144fps at 1440p no matter what chips you use.