how can i assign a node is not a clock

From the Quartus II Handbook:

"The Not a Clock assignment directs the Quartus II Classic Timing

Analyzer that the specified node is not a clock source when it would

normally be detected as a clock because of a global fMAX requirement. The

QSF variable for the Not a Clock assignment is NOT_A_CLOCK. This

assignment is not supported in the Quartus II TimeQuest Timing

Analyzer and there is no equivalent constraint. Appropriate clock

constraints are created in the Quartus II TimeQuest Timing Analyzer

only."

This assignment should not be required in TimeQuest. TimeQuest does a better job at recognizing which nets are clocks (and which are not) than the Classic Timing Analyzer does. If you think you have an application that requires this setting, please share it with us.