[Plugin: WTI Like Post] How can I add degree symbol after vote count?

Do you mean to use a degree image in stead of the thumb image. All the thumb images are being rendered from the images folder using the css file depending the style set in the plugin settings page. So if you need to use some other image, then replace the used images with your image (must have same dimension) in the images folder.

There is a setting to allow user to only like i.e. Show dislike option. You can use this.