CLIST is the task code being executed, so the syntax should look like:
R nn, 99task-code parameters
Specifies a reply number.
The reply number is shown in the system REPLY WITH REQUEST message displayed at the console. The REPLY WITH REQUEST message has the following format:
nn REPLY WITH REQUEST TO IDMS-DC Vnnnn
You can omit leading zeros from the number displayed in the system REPLY WITH REQUEST message.
Specifies that a task code follows a response to a prompt.
task-code Specifies the task code of a task defined on the system generation TASK statement.
task-parameters Specifies a command or any input parameters used by the task.
R 28, 99 CLIST DISCLIST
where DISCLIST is the clist name.
Documented in the System Tasks and Oper commands manual chapter 8.