Hello all! My question is: how can I check the computation time and optimality gap in a nonlinear model (using "mmxnlp")? Thank you :)

You can use Mosel's 'gettime' function to measure solve time, for example:

uses "mmxnlp", "mmsystem"
 
(...model statement...)
 
stime:=gettime
minimize(myobj)
writeln("Total solve time: ", gettime-stime, " sec")

For MIP problems you can calculate the gap value from solver parameters:

uses "mmxprs"
 
(...state and solve the problem...)
  
mipobj:= getparam("XPRS_MIPOBJVAL")
bbound:= getparam("XPRS_BESTBOUND")
relgap:= abs( (mipobj-bbound)/mipobj )

For general NL problems solved with local solvers, I don't think that you can obtain any really meaningful 'bestbound' value.