First of all, sketch mainly depicts the characteristics of the subject matter (such as angle difference, morphological transition and contrast). I'm sure you know all these basics, so I won't go into details.

I want to tell you: Yes, you should draw the wood grain.

The most obvious feature of a wood product or tree is its texture. When sketching, it has two functions: one is to enhance the volume of image quality, which refers to the visibility and intensity of sensory impact on the outline, texture and weight of the subject. Secondly, the grain shows the light sense of wood well, which is the most important thing.

I suggest that when sketching, don't show the lines on the glossy surface too clearly, but make wood marks at the junction of the backlit surface, so that the work will be more vivid.

Finally, I hope my suggestion can bring you some help, and I hope you can draw a good work. Thank you.