When I started to analyze this sentence: Wendell is here today. I saw that a linking verb is used and immediately I thought that the phrase which follows must be a subject complement. But while analyzing it I realized that I might be mistaken since after the verb an adverbial phrase is used: here today. So I got confused is it now a subject complement or an adverbial adjunct? Is in this case the verb is a linking verb?
Wendell is here today.
What adverbial phrase?
We have "here", which you might regard as an intransitive preposition or an unusual adjective. In phrases like "the weather here" and "this man here", it directly modifies a noun. We have "today", which you might regard as a fused prepositional phrase or as a noun in its own right.
On thing we don't have is the phrase "here today". Although that can exist as a phrase (it's hard to parse "here today, gone tomorrow" without regarding "here today" in that way) there's nothing to support that idea in this sentence. We can separate those words completely without any change to the sentiment of the clause:
Today Wendell is here.
That leaves us with "Wendell" as a subject, "is" as the copula, "here" as the subject complement, and "today" as an adjunct.