The examples of dramatic irony in this scene mostly revolve around Duncan and his praise of Macbeth and trust in him, even as Macbeth is already contemplating to kill Duncan to seize the crown himself. Let us just remind ourselves that dramatic irony is when the audience and one (or more) characters know something that another character or group of characters does not. Surely the most powerful example of dramatic irony in this scene comes at the end, when Duncan has announced that his eldest son, Malcolm, will inherit the crown after his death, and has given him a new title, the Prince of Cumberland. In an aside that reveals his feelings about this, Macbeth makes it perfectly clear that he is planning to kill Duncan to gain the power and position that he believes has been promised to him and is part of his destiny:
Stars, hide your fires!
Let not light see my black and deep desires;
The eye wink at the hand; yet let that be,
Whic the eye fears, when it is done, to see.
This is said in an aside just before he leaves to go to his castle and make preparations for the arrival of Duncan and his lords. What is ironic about this though is how Duncan closes this scene, praising Macbeth's character to Banquo:
True, worthy Banquo: he is full so valiant,
And in his commendations I am fed;
It is a banquet to me. Let's after him,
Whose care is gone before to bid us welcome:
It is a peerless kinsmen.
Duncan's assessment of Macbeth as being "full so valiant" and a "peerless kinsmen" clearly highlights his naivety and gullibility. He has already in this scene confessed that he is unable to distinguish between true loyalty and the mere appearance of loyalty in the case of the former treacherous Thane of Cawdor, and this is only underlined by the way he makes the same mistake with Macbeth.