how to split cell in keynote table, is it a drawback of keynote.

you can create the same effect of splitting a cell by adding an extra cell in other columns (this concept works in any of the iWork apps for a table):

1) Create a table (whatever size you need/want). I'm going to make the table in Numbers (because I do not like how tables work in Keynote):

Add a new table from the "Table Tool":

Once you have created a new table, add one more column than you actually want(In this case I want a table with 4 columns where one row has a split cell):

Select two cells in the first row:

Now, merge the cells using the Numbers menu item "Table > Merge Cells":

Now you can see that row 2 appears to have a split cell compared to row 1:

select row 1 by single clicking the row header (the "1" on the left), now copy. Now select rows "3" thru the end or as needed, paste:

It should look like:

select the table, copy, and paste it into Keynote. You can probably do this same procedure in Keynote.

A "Split Cell" tool is not available in Keynote, Numbers or Pages. You would have to do this manually, or use MS Excel or Libra Office.