I have a line image which Inkscape has difficulty seeing. How can I make the lines more pronounced/enhanced? 

Hi. Your request is vague. More details are needed.

Perhaps the quality of your image is not so good. Is the image a png file with transparency set?

Is the original image blurry?

Is the image an image of a line(s) with faint colors? Or with colors so close in hue that makes it hard to distinguish?

Does this same image appear "better" in your opinion in other applications?

Is it truly a bitmap (raster) image or an svg?

Are you trying to trace the image in Inkscape?

Can you upload the image for others to see and comment?