Hi, I need to maintain users profile in 2 databasase : DNN database, and an external database. An external database will get updated/inserted, if there are :
# Users update their profile
# new user register
# Users update their password

My plan is to make trigger for this. But I don't know in which table the users profile and password exist.

Could you kindly inform in what table is the user profile, and in what field is the password field??

Is there a particular reason that you need to maintain that information in two places? Generally that is not a good practice.

You might be better off creating a custom "authentication provider" that will use the data in the external table to authenticate users.

If you actually do need to keep this in two places, you might look into creating a custom "membership provider." You can then maintain everything programmatically, which should be easier and more predictable.

Look at the Professional DotNetNuke 4 and Professional DotNetNuke 5 for details on membership, role, and profile providers.

As an aside, I once worked on a project that included doing something similar to what you described. One of the rules was that I was not allowed to do it as a custom membership provider. It was a painful, and not entirely successful, project!