It's pretty clear Data can see, hear, and feel stimuli; in fact his sight is better than the average humanoid's. But what about his olfactory abilities? Can he smell or taste anything?
I've divided this answer into his abilities to taste and smell:
He can't taste...
In TNG 'Hero Worship', Data says
DATA: I would gladly risk feeling bad at times if it also meant that I could also taste my dessert.
This strongly indicates he can't 'taste' anything he eats or drinks.
...but he can detect
Nevertheless, I suspect he has the ability to detect chemicals ingested. In Generations he experiences 'hate' when he drinks a beverage. The only logical explanation of this is that he could detect the chemicals being ingested, which triggered an emotional response.
He can smell
It's alluded to a couple of times that he does have the ability to smell things:
- In TNG 'Phantasms':
DATA: Everything seems to remind me of the nightmare. Objects, sounds, smells. And now I have seen elements of the dream in a waking state. I cannot explain it.
- TNG 'The Offspring':
DATA: Yes, very good, Lal. You have correctly processed the sense of touch. There are many fascinating experiences I wish to share with you.
DATA: No, that is a flower, Lal. Inhale.
The above passage would also strongly indicate Data can smell.
So, I would expect Data can both taste and smell stimuli, at least in the form of having functional chemoreceptors. The full experience of taste and smells though elude him without the emotion chip, as all he experiences is analysis and identification of the presence of chemicals, a bit like a shopping list rather than a necessary sensation.
As we see in the episode TNG: Angel One, Data is perfectly capable of smelling, and accurately distinguishing a variety of smells:
Tasha pacing; Troi and Riker sitting; Data examining knickknacks. Data's attention falls on an atomizer. Squeezing the ball, he gets a face full of mist.
DATA: [Sniffs] Interesting. An alcohol-based synthetic, artificially reproducing a floral scent.
TROI: It is called perfume, Data.
and from TNG: The Most Toys
FAJO: The very first Basotile ever created by the Rodulans... centuries old. Priceless. A vase carved by the late Mark Off-Zel on Sirrie Four. The only known Roger Maris trading card from Earth circa 1962... smell it...
[Data does, reacts...]
FAJO: Bubblegum... I've preserved the scent...
Data is unable to read the label. He removes the cap and sniffs the contents... but still doesn't know what to make of it... he looks at the liquid and finally tells Scott the only thing he knows for certain.
I think the eternal rule for Data is he imitates almost all human capabilities, but can't "enjoy" them. I'll lay odds he could taste soup, tell you ingredient, in exact percentage, but couldn't tell you if it's delicious. He can probably identify breeds of roses by their smell, but can't say if he likes the scent. He plays violin, and can likely play any piece ever written, but can't any which one he thinks is better than the other.
I think Dr Soong would have given data the ability to detect bad smells at least. For instance if his cat (Spot) had left faeces or urine somewhere he would need to be aware of it.