I run modelsim gate level simulation for FPGA max10. I got error message: Module 'dffeas' is not defined. please let me know where can find 'dffeas'? ?

make sure you simulation all the libraries needed when you do vsim.

e.g.

vsim -t 1ps +transport_int_delays +transport_path_delays -L altera_ver -L cycloneiii_ver -L gate_work -L work -voptargs="+acc" countt

use the scripts help you to do this. For the FAE, can you look into the intel mainpage for this?