Swift Hackerrank Dynamic Array
The task is about dynamic arrays, and using an array (instead of a
dictionary, as you did) simplifies things considerably.

If you start with an array of numOfSequences empty arrays:

var seqList = [[Int]](count: numOfSequences, repeatedValue: [])


then the 1 x y query simplifies to

let seqIndex = ((x ^ lastAns) % numOfSequences)
seqList[seqIndex].append(y)


without the need to check for an empty dictionary value.

Some more suggestions:

Reading a list of integers occurs at two places in the program, that
justifies a separate function:

func readIntegers() -&gt; [Int] {
    return readLine()!.componentsSeparatedByString(" ").map { Int($0)! }
}


(Remark: Usually, forced unwrapping with ! should be avoided,
but here we have a programming challenge with well-defined input data.)

To increase the legibility of the code, I would assign the three
parameters of a query to variables type, x, y.
The code then becomes almost self-explaining.

The entire code then looks like this:

func readIntegers() -&gt; [Int] {
    return readLine()!.componentsSeparatedByString(" ").map { Int($0)! }
}

// Read  N(number of sequences) and Q(number of queries):
let input = readIntegers()
let (numOfSequences, numOfQueries) = (input[0], input[1])

var lastAns = 0
// Array of `numOfSequences` empty arrays:
var seqList = [[Int]](count: numOfSequences, repeatedValue: [])

for _ in 0..&lt;numOfQueries {
    let input = readIntegers()
    let (type, x, y) = (input[0], input[1], input[2])

    switch type {
    case 1:
        let seqIndex = ((x ^ lastAns) % numOfSequences)
        seqList[seqIndex].append(y)
    case 2:
        let seqIndex = ((x ^ lastAns) % numOfSequences)
        let index = y % seqList[seqIndex].count
        lastAns = seqList[seqIndex][index]
        print(lastAns)
    default:
        fatalError("Unexpected query")
    }
}