Hidden blobules are larger than normal ones and are bright reddish-orange in color. They are not that well hidden in general and you will likely see and gather most of them without even trying
This hidden blobule is found in Level 1-8. You will climb up to a catapult, launch into a tower, then go through a pipe. Launch off another catapult and into another tower. Get yourself up to where the second tower was and launch yourself to the right to the edge of the level. Zoom-out to see the ledge you are aiming for.