Kenneth Zohore put visitors Cardiff ahead and Derrick Williams levelled.
Warnock said: "Declan should have stopped the cross, Nooney's with his man.
"You live and learn, don't you? That's what we're doing - learning about next season and who you want on board."
Warnock also blamed himself for sending John and Noone on among only six substitutes, but said his bench choices were limited by injuries going into the game.
"Before the game you'd have taken a point, wouldn't you," he said.
"It's my own fault - I put the subs on. Two of them cost us the goal."
Overall Warnock has been pleased by Cardiff's progress since his arrival in October and offered praise to striker Zahore and full-backs Jazz Richards and Joe Bennett
"I think Kenneth Zahore can get better and he's got to try and last the games as well fitness wise," the manager said.
"I mean you can't fault him - 80 minutes the way I'm asking him to move about and he's got such a big frame as well, but he's enjoying it.
"I love him. He's got blood all over his socks, it's brilliant, isn't it? I like that."
The Cardiff boss was equally impressed by full-backs Richards and Bennett, saying they were "fantastic".
He added: "I said to them before the game 'if you two come out of this game and I say well done to you, we'll have got at least a point and probably win'.
"And I thought they were super.
"Jazz Richards played the best since I've arrived and if I'm honest, I didn't think Bennett could defend like that.
"I thought he was superb so it augurs well."
The Bluebirds were second from bottom of the Championship at that point.
"When you think where they were, you wouldn't think it was the same bunch of players - they've been excellent," he said.
"We didn't sign anyone in January. For the future we know where we're looking and if we can just improve one or two areas with quality I think we'll be as good as anyone, no matter how much other teams spend."
The draw at Blackburn came on the day Cardiff's accounts showed a near £9.5m loss for the financial year ending May, 2016.
Manager Neil Warnock hinted Declan John and Craig Noone's Cardiff City's futures are in doubt after holding them responsible for Blackburn's late equaliser in their 1-1 draw.