The ornamental design for a portion of a display with a graphicaluserinterface, as shown and described.
The FIGURE is a front view of a portion of a display with a graphical user interface, showing my new design.
The broken line showing of the display is included for the purpose of illustrating portions of the article, and the broken line showing of portions of the graphical user interface is included for the purpose of illustrating environmental structure, the broken lines form no part of the claimed design.