First, make the k sound by raising your back of the tongue to touch the soft palate. next, make the OU diphthong sound.( there are 2 type of OU sound, i.e
British and American type. I'll teach you the first one as there's many british speaker here. The British one is the combination of /ə/ as in "ago" and /ʊ/ sound as in ''Book''. Next, to make the /l/ sound, do the same as you make the t and d sound. (That's what I've been told).
but when I hear native speakers and talking dictionaries to speak these words, sometimes the sound would be changed to "t" sound, not the "d" sound, could any people explain this to me?
As for this question, I can hardly tell you because I'm not a native speaker. I'm just a learner like you. Can you give me some example about that situation? Probably I can answer you WHY.