There is nothing in Job 38:14 that states the earth is flat unless you just want to analyze the first part of 14 and nothing else but that is taking something out of context. So let’s put things into context by looking at the whole thought, starting in verse 12 ending in verse 15.

Verse 12 and 13 "Hast thou commanded the morning since thy days; and caused the dayspring (dawn) to know this place; that it might take hold of the ends of the earth, that the wicked might be shaken out of it (KJV)? These two verses God is asking Job a question, is Job in command of the mornings and the effect the dawn has on the wicked of the earth? For example the thief in the night is now exposed by the light of the morning and can no longer use the night to do his evil deeds. Verse 14 ""It is turned as clay to the seal; and they stand as a garment (KJV). Now, hopefully there is an understanding that the subject is the light and not the shape of the earth. If someone takes a seal (stamp or a signet ring) and pushes it into the clay or wax it leaves a distinct impression of an image (yes, and flattens it but that is not what it is referring to). When the stamp is removed one can clearly see the emblem, like the writer states "and they stand as a garment". Have you ever been camping in the woods? At night the surrounding area looks like a big mass of something and there is no true distinction of the things around you. When morning comes and the light shines one can start to distinguish the different objects. This is what the verses state, verse 15 also makes mention of light before going on to a new question in verse 16.