Use a try/except, if we cannot cast to an int it will set is_dig to False:

try:
    int(question)
    is_dig = True
except ValueError:
    is_dig = False
if is_dig:
  ......

Or make a function:

def is_digit(n):
    try:
        int(n)
        return True
    except ValueError:
        return  False

if is_digit(question):
   ....

Looking at your edit cast to int at the start,checking if the input is a digit and then casting is pointless, do it in one step:

while a < 10: 
     try:
        question = int(input("What is {} {} {} ?".format(n1,op,n2)))
     except ValueError:
        print("Invalid input")
        continue # if we are here we ask user for input again

    ans = opsop
    n1 = random.randint(1,9)
    n2 = random.randint(1,9)
    op = random.choice(list(ops))

    if question ==  ans:
        print ("Well done")
    else:
        print("Wrong answer")
    a += 1

Not sure what Z is doing at all but Z = Z + 0 is the same as not doing anything to Z at all 1 + 0 == 1

Using a function to take the input we can just use range:

def is_digit(n1,op,n2):
    while True:
        try:
            n = int(input("What is {} {} {} ?".format(n1,op,n2)))
            return n
        except ValueError:
            print("Invalid input")


for _ in range(a):
    question = is_digit(n1,op,n2) # will only return a value when we get legal input
    ans = opsop
    n1 = random.randint(1,9)
    n2 = random.randint(1,9)
    op = random.choice(list(ops))

    if question ==  ans:
        print ("Well done")
    else:
        print("Wrong answer")

The way to convert to integers is to try the conversion and be prepared for it to fail:

for i in range(len(mylist)):
    try:
        mylist[i] = int(mylist[i])
    except ValueError:
        pass

Instead of checking if you can convert the input to a number you can just try the conversion and do something else if it fails:

choice = raw_input("> ")

try:
    y = int(choice)
    x += y
except ValueError:
    print "Invalid input."