Can I generate script of a migration with EF code first and .net core

As per EF documentation you can use Script-Migration command.

If you want to just script all the migrations you can simply call it from Package Manager console like that. If you want to just script the changes from the last migration you can call it like this:

Script-Migration -From <PreviousMigration> -To <LastMigration>

Be sure to check the docs, there're a few more options to the command.

dotnet ef migrations script --help

Usage: dotnet ef migrations script [arguments] [options]

Arguments:
  <FROM>  The starting migration. Defaults to '0' (the initial database).
  <TO>    The ending migration. Defaults to the last migration.

Options:
  -o|--output <FILE>                     The file to write the result to.
  -i|--idempotent                        Generate a script that can be used on a database at any migration.
  -c|--context <DBCONTEXT>               The DbContext to use.
  -p|--project <PROJECT>                 The project to use.
  -s|--startup-project <PROJECT>         The startup project to use.
  --framework <FRAMEWORK>                The target framework.
  --configuration <CONFIGURATION>        The configuration to use.
  --runtime <RUNTIME_IDENTIFIER>         The runtime to use.
  --msbuildprojectextensionspath <PATH>  The MSBuild project extensions path. Defaults to "obj".
  --no-build                             Don't build the project. Only use this when the build is up-to-date.
  -h|--help                              Show help information
  -v|--verbose                           Show verbose output.
  --no-color                             Don't colorize output.
  --prefix-output                        Prefix output with level.

so,you can try

dotnet ef migrations script ver1 ver2
dotnet ef migrations script ver1 ver2 -o ./script.sql

This works in .Net Core 2.1