Is it grammatically correct.

[David1999]

Is it grammatically correct to write

Can you advise us the number of days you spent in Thailand last year?

Thanks

[Cerberus™]

No: you should use a different verb, such as "tell".

[David1999]

Thanks. This sentence is for professional advice, so we better use the verb 'advice' rather than 'tell'.

[Cerberus™]

It is often thought that using longer words can improve your language; but it cannot. Most good writers prefer the short word over the long one, the normal over the formal - unless there is a clear reason why the more complicated word would better express the writer's thoughts. You shouldn't use colloquial expressions in formal situations, that much is true; but normal expressions are fine.

If you want to toss "tell", how about this one: "How many days did you spend in Thailand last year?". If you insist on using a "formal" word, you could say "Please inform us of the number of days you spent in Thailand last year.". The verb "to advise" has a different meaning; I do not see how it could be used here.