My first thought was to give someone props : give props to (one) To praise one and show them respect.
Thank you, but I have to give props to Jeanne, who organized this entire event for us.
(TFD) props noun, ( usually used with a singular verb)
Slang.
proper or due respect or recognition; credit: I give him props for putting up with annoying customers.
(Dictionary.com)
That's well-known here in the US.
There's a relevant post on ELU:
What's the etymology of “props”?
Notice that props itself is not used as a verb in this sense.
We don't *prop or *props someone to mean that we praise them.
ell.stackexchange.com/users/36187/Em.
Kudos is originally used to praise and honor someones achievements, but is also used to show respect in popular culture nowadays.
For example, you could congratulate your friend on passing a test by saying: Kudos to you for passing that test!
That is quite a feat.
Be mindful that kudos is a singular form, even though it looks like a plural.
ell.stackexchange.com/users/64503/Lars Mekes
Big-up or Big-ups is used to acknowledge respect
ell.stackexchange.com/users/69171/hairmot
The term diss is certainly slang.
All dictionaries that I checked list it as such.
So, the opposite of it should probably also be a slang word.
Thus, one possible antonym of the word diss that you might consider would be the term respek (see definition #4 in Urban Dictionary) which was popularized in the early 2000s by the satirical fictional character Ali G portrayed by British comedian Sacha Baron Cohen.
And it can definitely be used as an inside term (a term that's typically understood only by people who know certain facts and context).
Examples: Stop dissing me, man.
Instead, show me some respek . — I nailed his ass five times in a row in Warcraft today. — Total respek , man!
Ali G talks about how respek is important (don't forget it's comedy): https://www.youtube.com/watch?v=Vqtg_JFGh6I
ell.stackexchange.com/users/6450/Michael Rybkin
I have heard ‘spec’ used in UK as a positive reinforcement of a person’s integrity, a shortened form of ‘respect’.
ell.stackexchange.com/users/69172/Steve
You mention that diss is slang.
You didn't mention whether you wanted your result to be slang.
Here are some less slangy results: prop (as in "prop him up", slightly different than "give him props" as noted in Max's answer )
give kudos [to] (again, a variation of usage from another answer,
this time Lars Mekes's answer ) several others: compliment, envy / be jealous, follow, praise (or "singing his praises"), glorify, honor, elevate, dignify, give homage, venerate
ell.stackexchange.com/users/17653/TOOGAM
"Stroking" is verbally boosting someone's ego, with praise or gushing admiration or fawning.
It seems to me the perfect absolute antonym to "diss", which isn't just about disrespect, it's about trying to tear someone down and damage their ego.
"Bob, that was really the best, your stuff is the best, you're the best."
"Aww, Betty, thanks
but you really don't have to stroke me like that."
ell.stackexchange.com/users/56062/Beanluc
Word Sometimes: word up From generally the same culture as 'diss' comes the single word exclamation: word, signifying respect or agreement with the person spoken to.
The Urban Dictionary definition of "word" is "Word"
has no single meaning, but is used to convey a casual sense of affirmation, acknowledgement, agreement, or to indicate that something has impressed you favorably .
ell.stackexchange.com/users/89/mcalex
Diss can be used as a verb or as a noun.
Similarly, it's antonym should be the same.
Complement is the closest word I can think of.
He dissed me.
He complimented me.
That's a bad diss.
That's a good complement.
ell.stackexchange.com/users/69277/Wisani
I learn that 'diss' is a shortened version of "disrespect" Urban Dictionary: diss   For example, try to diss me, man.   What's the opposite of it? I searched 'spect' as shorthand for 'respect'. Nevertheless, it does not feel as strong and smart as 'diss'  Note: 'Diss' is a extremely popular in China as cyberspeak for joking with each other.
The antonym of "diss"
ell.stackexchange.com
<word-request><slang><antonyms>
ell.stackexchange.com/questions/155549
ell.stackexchange.com/users/64925/Calculus
Kudos  was originally used to praise someone's achievements, but is also used to show  respect  in popular culture nowadays.  For example, you could congratulate your friend on passing a test by saying:   "Kudos to you for passing that test!", meaning "That is quite a feat". Kudos is originally used to praise and honor someones achievements. 
Kudos is originally used to praise and honor someones achievements. It is also used to show respect in popular culture nowadays. Be mindful that kudos is a singular form, even though it looks like a plural.