The ornamental design for a surfacepattern of a paper product, as shown and described.
The sole FIGURE is a top plan view of a surface pattern of a paper product showing my new ornamental design wherein the broken lines indicate that the design may continue indeterminately in one or more directions. The design repeats uniformly throughout the length and width of the paper product, such as a sheet of a paper towel or tissue product. A specific length and width of the paper product forms no part of the claimed design. The broken lines in the FIGURES form no part of the claimed design. The surfaces or portions not shown in the drawings or described in the specification form no part of the claimed design.