I'm curious to know how do you remember the port number information, which tool to use when scanning for vulnerabilities? I'm really bad in domain 6 and hope can have someone to guide me in this chapter.
Thank you very much.
Remembering TCP port numbers comes with experience/familiarity. It'd be common over time to know which ports common service like FTP, SSH, Telnet, SMTP, TACACS, DNS, HTTP, Kerberos, LDAP etc run on. In terms of tools for scanning you might also want to look at C|EH.
Everyone learns differently but I think that if you really don't know any of them, you should try flash cards, quizzes, and maybe even dig in a little further and open up a firewall to test with and configure them, adding notes as you do it. I think it is more important to know the differences between port types, and what is secure and not secure. TCP vs UDP. FTP, SFTP, SSH, etc.
There are also some videos if you search for them that could help but since they are with another cert body I will not publish the links directly in here.