You for sure do not want to shoot too light or heavy pellets, i do not have this rifle but i would assume it can match my decade + old FX cyclone in power, so 15/16 - 18 grain JSB domed pellets should fly good, and probably also the JTS pellets ( domed ) i tried last summer in my Cyclone
If you grab some random cheap weird brand pellet, then you will not shoot that well, i for instance have never seen pointed pellets fly good in anything, my friend do have success with flat head pellets in some rifles but at moderate distances.
The chronograph, is a good tool, but you can also do it the old way by just finding the one or few pellets the rifle shoot well with and then just stick to those, and so not needing to tune / adjust on your rifle.
If you do get a chronograph, either shoot thru model like you posted picture of, or smaller attach to rifle kind, you will probably see that speeds in the 800 - 900 FPS range is working good.
Many of us still have a pellet collection so we have umpteed brand / models / weights of pellets to try in a new rifle, even if today many rifles are adjustable and so you have a chance of tuning speed a little and so maybe get a marginal pellet to shoot good too.
In a .22 15 - 18 grain is good middle weights today, though some tins will say heavy / jumbo heavy, the really light ones in general are just for old anemic rifles or rifles tuned down to have a larger shot count on a fill.