Welcome!
The bike needs to be level for the oil to be checked accurately. If you have an older ninja 250, the centerstand (NOT the sidestand) should work well enough for this. If not, have a friend hold it upright.
Also, the oil should be inbetween the indicators. I've circled them in red:
Anywhere inbetween the indicators is good, just be sure to check the level regularly. The oil looks overfilled to me, which will create too much pressure inside the engine, and possibly causing damage (or causing it to spit out the oil and making a mess. I can't remember if the ninja has this feature or not).