How to get more detailed exception in ABP?

Check error in Logs.txt.

From the documentation on Logging:

Configuration

All configuration is done for Log4Net when you create your application from ASP.NET Boilerplate templates.

...

It's defined in the log4net.config file of the application as shown below:

<?xml version="1.0" encoding="utf-8" ?>
<log4net>
  <appender name="RollingFileAppender" type="log4net.Appender.RollingFileAppender" >
    <file value="Logs/Logs.txt" />

You can simply send the exception details to the client by enabling one of ABP's configurations (SendAllExceptionsToClients) in ***.Web.Core Module, like this:

public override void PreInitialize()
{   
    Configuration.Modules.AbpWebCommon().SendAllExceptionsToClients = true;
}

Then you get the exception details on the client. Recommended only during development.