That's pretty close, but there are a few subtle errors.
Where you have "flq_" you need "flg_" - flg is short for 'flag'.
You want to check for a cbet on the flop (not preflop) so you need to use flg
_f_cbet.
You're also missing the "s" off the end of the database table name "holdem_hand_player_statistic
s".
Actions strings need to be in single quotes instead of double quotes. 'BF'.
You're missing the word "if".
When writing expressions you may find it easier to use the "insert" link, which allows you to find the appropriate parts of the expression and make sure they are entered correctly.
This is the expression you want:
sum( if[ holdem_hand_player_statistics.flg_p_3bet AND holdem_hand_player_statistics.flg_f_cbet AND lookup_actions_f.action LIKE 'BF', 1 , 0 ])
Check out the
Tutorial: Custom Reports and Statistics for more information.