I have a jpg image showing pencil drawings and writing made on a plywood surface. I want to enhance the image to make the pencil markings more distinct and make the wood grain and wood color less distinct

This one is  tough.

I opened the image in Camera raw (File>open as, and in the dialog select Camera raw in the drop-down)

Work the sliders to best advantage, esp. temperature, tint, blacks

Then, "open image" @ bottom right to open it in conventional PSE, and refine further with Levels adjustment layer.