It is said that no one knows when, where, and how they will die, but ʻUthmaan, may Allaah be pleased with him, knew that he would be killed and also dreamt that the prophet, sallallaahu ʻalayhi wa sallam, told him that if he continued his fast, he would break it with him. It seems contradictory, and Allaah knows best. Can u answer my question directly please?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah and that Muhammad, sallallaahu ʻalayhi wa sallam, is His slave and Messenger. 

The knowledge of the time and place of one's death is among the matters of the Unseen of which the knowledge is the domain of Allaah exclusively, as stated in the hadeeth narrated on the authority of ʻAbdullaah ibn ʻUmar in which the Prophet, sallallaahu ʻalayhi wa sallam, said, "The keys of the Unseen are five." He, sallallaahu ʻalayhi wa sallam, then, recited the verse that reads (what means): {Indeed, Allaah (alone) has knowledge of the Hour and sends down the rain and knows what is in the wombs. And no soul perceives what it will earn tomorrow, and no soul perceives in what land it will die. Indeed, Allaah is Knowing and Acquainted.} [Quran 31:34]" [Al-Bukhari]

Ibn Hajar wrote:

“Al-Qurtubi said: Based on this hadeeth, no one can claim having knowledge of these five matters. The Prophet, sallallaahu ʻalayhi wa sallam, explained the verse: {And with Him are the keys of the unseen; none knows them except Him...} [Quran 6:59] as referring to these five matters; and the relevant hadeeth is cited in Saheeh Muslim. Whoever claims to know any of these matters of the Unseen is a liar unless such knowledge was imparted to him by the Prophet, sallallaahu ʻalayhi wa sallam...” [Fat-h Al-Baari]

The Prophet, sallallaahu ʻalayhi wa sallam, did not have knowledge of the Unseen, except for what Allaah revealed to him, as clearly stated in the verse: {(He is) Knower of the unseen, and He does not disclose His (knowledge of the) unseen to anyone, except whom He has approved of messengers, and indeed, He sends before each messenger and behind him observers.} [Quran 72:26-27]

The source of ʻUthmaan's knowledge that he would die as a martyr was the Prophet, sallallaahu ʻalayhi wa sallam, and this knowledge was imparted to the Prophet through divine revelation. This incident is an example of the exception stated in the verse: {Except whom He has approved of messengers...}

It should be noted that one might have a dream indicating the approach of his death, but he cannot be sure as to when exactly he will die. It has been reported that ʻUmar said, “I saw in a dream that a cock was pecking me thrice, and I feel that it means that my death is near.” [Muslim]

For more benefit, please refer to fatwa 291049.

Allaah knows best.