How can I assign a node is not a clock for TimeQuest

Not really understand what you trying to do but have some inputs to your questions. Is there any way to let Quartus TimeQuest know it's not a clock? No SDC can tell that it's not a clock signal. Once a signal connected to any clock port of FF will be deemed as clock signal in the check rule of TQ. You either ignore it in the report or assign it with clock constraint. What's the reason that I couldn't find the node for signal_clk, may because there is no flip-flop that it's regarded as the PIN itself? Yes, it's likely to be synthesized away since the "PIN" is connected directly to "signal_clk" . Anyhow, you can preserve that signal after post-fit using synthesis attribute https://www.intel.com/content/www/us/en/programmable/quartushelp/17.0/hdl/vlog/vlog_file_dir.htm, perserve