Prepositions at the end of a sentence [duplicate]

I get struggled in choosing to put or not to put a preposition at the end of the sentence. I feel like it's optionally, but I'm not sure, so I'm asking. The question is, should I put prepositions in these sentences and why?

What am I guilty of?

It's nothing compared to what I could be asking for.

Whom are you talking to?

It seems a big theme (prepositions at the end or the start of a sentence), that is why I would like to thank you even if you explain to me at least these cases.

Putting prepositions at the end of the sentence is called "stranding". Your three sentences are examples of stranding.

The alternative is called "pied-piping", which refers to the placement of the preposition in front of an interrogative or relative pronoun. So the preposition can be pied-piped in the first and third of your sentences, which start with interrogative pronouns, resulting in:

• Of what am I guilty?
• To whom are you talking?

An example of stranding/pied-piping in a sentence with a relative pronoun is:

• The parcel (which) I was waiting for never arrived. (stranding)
• The parcel for which I was waiting never arrived. (pied-piping)

Your second sentence preposition cannot be pied-piped without producing dubious syntax. For example:

• ?It's nothing compared to that for which I could be asking.

Garner in his Modern American Usage (p654) discussion of the topic reminds us of Winston Churchill's famous:

• That is the type of arrant pedantry up with which I shall not put.

and says that the avoidance of stranding "sometimes leads to just such a preposterous monstrosity".

Furthermore, there are numerous cases where the preposition simply cannot be pied-piped. For example in what are called prepositional verbs or phrasal verbs, among other terms.

• People all over the world are being advised to stay in.

So, you can safely ignore the advice, wherever it is coming from, that preposition stranding should be avoided. Fowler, in Modern English Usage (p473) calls the rule a "cherished superstition. Language Log calls it a zombie rule.

Nevertheless, there are three occasions when pied-piping is to be preferred to stranding. Steven Pinker in The Sense of Style (p221) discusses these. Firstly, in formal contexts. Pinker cites a passage from Lincoln's Gettysburg Address:

...increased devotion to that cause for which they gave the last full measure of devotion (pied-piping)

contrasting it with the weaker

...increased devotion to that cause which they gave the last full measure of devotion for. (stranding)

The second context in which pied-piping is to be preferred is when, in Pinker's words,

...a stranded preposition would get lost in a hubbub of little grammatical words, such as One of the beliefs which we can be highly confident in is that other people are conscious. The sentence is easier to parse when the role of the preposition is settled before we get to that busy crossroads: One of the beliefs in which we can be highly confident is that other people are conscious.

The third context in which preposition stranding results in weaker prose is related to the concept of end weight, whereby "heavy" phrases often work better at the end of sentences than, for example, lightweight prepositions. Pinker quotes a sentence from Bernstein in which the stranded preposition sounds like "the last splutter of an engine going dead":

"He felt it offered the best opportunity to do fundamental research in chemistry, which was what he had taken his Doctor of Philosophy degree in."

In summary, preposition stranding is generally to be preferred in informal spoken and written language. In formal written language pied-piping may be the better choice.