There are two specific moments that I find directly relevant here:
"Encounter at Farpoint"
The very first time Picard calls Riker "Number One" is in "Encounter at Farpoint", on the bridge, at around 1:16:00. The actual dialog spoken was:
PICARD: At least you impressed him, Number One. That's hopeful.
RIKER: Thank you, Captain. Captain, if he's not open to evidence in our favour, where will you go from there?
PICARD: I'll attend to my duty.
Although, the original script differs slightly:
PICARD: (nods) But I had a feeling you impressed him, Number One. That's hopeful.
RIKER: Thank you, Captain, That's the first time you've called me "Number One".
PICARD: (small smile) I believe I'll enjoy getting to know you, Bill. If we live long enough.
I am not sure why this scene was changed in the final production but it does pretty clearly indicate that the writers at least intended Riker to be pleased by (or, certainly, not displeased by) the moniker.
(As an aside, kind of funny that Picard calls him "Bill" in the original script. As far as I know, the only times he was actually referred to as "Bill" in production dialog was by Troi -- in "The Naked Now" and "Haven" -- and Tam calls him "Billy Boy" in "Tin Man".)
Years later, in the opening sequence of "The Pegasus", where they're setting up for "Picard Day", Riker picks up a little Captain Picard doll and imitates Picard's accent:
PICARD: I don't know why we have to do this every year. I thought that last year the teachers had agreed that they wouldn't do this anymore.
TROI: Captain Picard Day is one of the children's favourite school activities. They look forward to it all year.
PICARD: Why does it have to be me?
TROI: Because you're the Captain, and they look up to you. You're a role model for them.
PICARD: Well, they seem to have a somewhat exaggerated impression of me.
RIKER: (imitating Picard and using a doll) I don't know. I think the resemblance is rather striking. Wouldn't you agree, Number One?
PICARD: Isn't there something else you have to do?
RIKER: I'll be on the Bridge.
(starts to walk off with a Picard doll)
(Riker puts the doll back and leaves)
This isn't really a direct comment but it does indicate that Riker views this as one of the defining characteristics of his interactions with Picard (imitation is a good hint at how a person views another person). Also, he does the imitation in pure jest, suggesting that he finds it endearing or at least amusing, rather than having any resentment about it.
Note that this is season six, Riker and Picard have been serving together for a while at this point and are comfortable with each other.
Incidentally, I'm almost certain this is the only time Riker speaks the actual phrase "number one".
So as for your question:
Has Riker made it known if he likes/dislikes being called "Number One"?
Never explicitly, although he has certainly implied that he accepts it and possibly finds it amusing or endearing. He responds to it on the regular, to the point where he almost seems to accept it as a nickname. He most definitely has never explicitly or implicitly expressed dislike. Furthermore in the original Farpoint script he seems pleased, and even in the production dialog he does not object.
So we can say for certain that he at least doesn't mind it, and definitely identifies to it.
(Sources: Memory, seeing the series a dozen times, and I searched series and movie production scripts for "number one", read the dialog for Riker's reactions and checked the more interesting ones for tone and facial expressions in the episodes themselves. I did not, however, review any interviews, writers notes, etc., and would be curious if anybody knows of any mentions of this in such material.)