No, it is not.
The word today is a possessive in the noun phrase "today's meeting" (meeting happening today). The word today is an adverb in the verb phrase "meeting today" (occurring today). The latter is unusual but not unseen in sentences such as "The President will be today meeting with his Cabinet" instead of "The President will be meeting with his Cabinet today" especially if there is a longer object such as "meeting the most vocal critics of his plan to end the ongoing crisis" where the "today" could be too far from the verb modified. More typically, the "today" is used to start the sentence.
The correct phrase is "today's meeting." Using the possessive form "today's" indicates that the meeting is happening on the specific day that is being referred to.
Yes, that sentence is grammatically correct. It effectively conveys the message that all the meetings you had planned for today have been canceled.
It is. In American English, the preferred past tense of cancel is "canceled" with one L, whereas other English speaking countries such as the United Kingdom, Canada, and Australia, the preferred past tense is "cancelled" with two L's. Both are technically correct in all countries and one L versus two is a stylistic choice.
"We were informed it will be corrected today" is a correct sentence. However, it might sound a little better to say "We were informed that it will be corrected today."
They didn't have time to have the meeting today so they had to postpone it.
If it's just those four words, then it should be "Who is here today?" If it's part of a longer statement, then either could be correct, depending on if it's plural or singular. "The boys who are here today" "The boy who is here today."
A question mark is used at the end of a sentence to indicate that it is a question. Do you understand? How are you today? What time is it? Is today the day of the meeting?
I prefer: 'Delivery is scheduled for today.'
I was so embarrassed when I forgot your name at the meeting today.
The correct grammar for the sentence is: "This hole is closed today for maintenance."
It is correct.