You could add a number attribute to your cell actor called "ID" (e.g.). When the cells are created, set the ID for each actor, using the block "behaviors"-->attributes-->for last created actor set "ID" to x.
Next I would make a new list that stores all the players input, so make it a list that has as many items as your solutions list (I guess it's always 9 in Soduko :-) ), set each item to 0.
Now you need one more attribute to check which cell is activated, for simplicity I would just make a game attribute called "chosen cell".
Now you can add to your cell behavior:
when mouse is pressed
-if mouse is down on self
--set "chosen cell" to ID
Then when a key is pressed
replace item "chosen cell" in "player input list"
Now when checking for the solution all you have to do is compare the lists:
Set a boolean called "solution correct" to true
Set a number attribute "item" to 0
Repeat 9 times
-If NOT get item 'item' from list 'solution' = get 'item' from list 'player input list'
-set 'solution correct' to false
-increment 'item' by 1
After the loop you check if the 'solution correct' boolean is still true, if so, the game was solved.
Instead of the loop you could use the "each item in list" block, but I had some issues with that so I prefer to just make a loop.