I've finished all the main Thieves Guild quests and must have done all of the special jobs from Vex and Delvin 8 or 9 times each. Even so, all Brynjolf ever tells me is that he's busy and that we'll talk later. How exactly do I get the quest "Under New Management" to initiate?

Edit: As far as I know I just have to do the other jobs several times and then the "special jobs" become available. I just haven't reached that point yet I suppose.

You have to do 5 special jobs in Whiterun, Windhelm, Solitude and Markarth.

The quickest way to do it is to abandon quests from the holds you no longer need to complete, and quests from riften as they count for nothing. Keep abandoning them until you get special jobs for the hold you need.

Example: Say you have done 4 special jobs in Windhelm and 5 in whiterun, abandon all the whiterun jobs until you get windhelm jobs.

Like Eterna said, the last few quests become available once you do 5 quests in the other major holds. Once you do those you will be rail-roaded into doing a particular quest for that city.

Easiest way for me to get the quests in the city I wanted was to quick-save before talking to Vex/Delvin, and re-load if I didnt get what I wanted.. You could just abandon the quest to & pick another one.

Sorry for being off-topic but how do you exactly abandon quests? I sometimes start quests that I don't want to, and just toggle them off, but the list is getting kinda long in my quest journal...

Just keep refusing jobs and ask for a different type of job when you ask again, till you get the one in the city you need.

Can the random jobs you do always be of the same type? For example, can I just keep doing numbers jobs to complete the required 5 quests in a city?

Also, is there any way to tell how many of the random quests you've already done for each city without actually writing it down?