Highlight the white text inside the block for hints ranging from vague to specific...
When drawing the path, indicate direction of travel on each segment to help solve this.
Some paths can be drawn in immediately; e.g. between the U and k and s, since there is only one path into and out of the k. Note that you can also tell the direction of travel due to the lower-case to lower-case rule.
The upper left corner has to be R-->v-->o because of the v having only one entrance and exit..
The lower right corner has to be M-->z-->h-->G-->b-->Z because of the h having only one entrance and exit..