Say it as two words, dot com, with stress on com. British English: /dɒt kɒm/. American English: /dɑt kɑm/.
In example dot com, the full spoken address, keep the same stress: a light dot, a stronger com.
Mouth movements for the sequence
Say it as two words: dot com. Stress falls on com. British English: /dɒt kɒm/, with both vowels matching the vowel in lot. American English: /dɑt kɑm/, with both vowels close to the vowel in father but shorter.
Where no variety is specified, /dɒt kɒm/ and /dɑt kɑm/ are both accepted pronunciations; pick one and keep it consistent within an address.
Dot com in a spoken address
Contrast the pair side by side: with the dot, say dot com; without it, say example com. Both keep the stress on com, so the only change is dropping dot when the address leaves it out.
Go to example dot com for the details. The sequence flows between the name and a pause.
Which dot com is it? The second word carries the beat again in a question.