Corn Plant with Yellow and Brown Spots
The brown spots might be due to injury to the leaves. This might have happened in handling or repotting. Make sure new leaf tips do not touch walls or other objects.
The yellowing may be due to improper watering. Allow the soil to dry slightly between waterings. Use your finger to feel the soil about half an inch deep. When it feels dry, it's time to water. Also, make sure there is adequate drainage at the bottom of the pot. The pot should be set on a few stones or marbles to prevent it from sitting in the drained water.
I hope this helps!