The word(s) "doubt" appears 83 time(s) in 78 verse(s) in Quran in Abdullah Yusuf Ali translation.

(11) That they said (in boast), "We killed Christ Jesus the son of Mary, the Messenger of Allah";- but they killed him not, nor crucified him, but so it was made to appear to them, and those who differ therein are full of doubts, with no (certain) knowledge, but only conjecture to follow, for of a surety they killed him not:-

(12) O ye who believe! When death approaches any of you, (take) witnesses among yourselves when making bequests,- two just men of your own (brotherhood) or others from outside if ye are journeying through the earth, and the chance of death befalls you (thus). If ye doubt (their truth), detain them both after prayer, and let them both swear by Allah: "We wish not in this for any worldly gain, even though the (beneficiary) be our near relation: we shall hide not the evidence before Allah: if we do, then behold! the sin be upon us!"

(13) He it is created you from clay, and then decreed a stated term (for you). And there is in His presence another determined term; yet ye doubt within yourselves!

(14) Say: "To whom belongeth all that is in the heavens and on earth?" Say: "To Allah. He hath inscribed for Himself (the rule of) Mercy. That He will gather you together for the Day of Judgment, there is no doubt whatever. It is they who have lost their own souls, that will not believe.

(15) Say: "Shall I seek for judge other than Allah? - when He it is Who hath sent unto you the Book, explained in detail." They know full well, to whom We have given the Book, that it hath been sent down from thy Lord in truth. Never be then of those who doubt.

(16) If there had been immediate gain (in sight), and the journey easy, they would (all) without doubt have followed thee, but the distance was long, (and weighed) on them. They would indeed swear by Allah, "If we only could, we should certainly have come out with you": They would destroy their own souls; for Allah doth know that they are certainly lying.

(17) Only those ask thee for exemption who believe not in Allah and the Last Day, and whose hearts are in doubt, so that they are tossed in their doubts to and fro.

(18) But those in whose hearts is a disease,- it will add doubt to their doubt, and they will die in a state of Unbelief.

(19) This Qur'an is not such as can be produced by other than Allah; on the contrary it is a confirmation of (revelations) that went before it, and a fuller explanation of the Book - wherein there is no doubt - from the Lord of the worlds.

(20) If thou wert in doubt as to what We have revealed unto thee, then ask those who have been reading the Book from before thee: the Truth hath indeed come to thee from thy Lord: so be in no wise of those in doubt.