The wikipedia entries contain very good information on both and can help getting rid of your confusions:
DomainKeys
DomainKeys (informally DK) is a deprecated e-mail authentication
system designed by Yahoo1 to verify the DNS domain of an e-mail
sender and the message integrity.
Aspects of DomainKeys, along with parts of Identified Internet Mail,
were combined to create DomainKeys Identified Mail (DKIM),2[3][4]
which is now widely used.[5]
Both DomainKeys and DKIM were published in May 2007, DomainKeys as an
"historical" protocol, and DKIM as its standards-track replacement.
DomainKeys Identified Mail
DomainKeys Identified Mail (DKIM) is an email authentication method
designed to detect email spoofing by providing a mechanism to allow
receiving mail exchangers to check that incoming mail from a domain is
authorized by that domain's administrators.1 It is intended to
prevent forged sender addresses in emails, a technique often used in
phishing and email spam. DKIM allows the receiver to check that an
email claimed to come from a specific domain was indeed authorized by
the owner of that domain which is done using cryptographic
authentication.
DomainKeys Identified Mail (DKIM)
As you can see, DKIM is the current standard and was developed as a replacement for Domainkeys. So, you don't need both and having DKIM is enough.