In general, the pipe symbol, "|" is used to separate values when more than one option is selected. For DXDMES the question is, "If Mild Cognitive Impairment, select any that apply:" If the participant demonstrated multiple features then both options 1 and 2 would be selected and the answer captured as "1|2"
You can download the Case Report Forms from the DOWNLOAD | Study Data section to see contextual information about the questions/answers.