Solution to 25D has been deliberately left unsolved and is to be answered only by a non-regular / novice commenter, with proper annotation. Those who have answered earlier in the week, please give others a chance.
ACROSS
9 View broadcast at one, live (9) ELEVATION*
10 Enquire about missing Indian Railways card (5) QUEEN ENQUirE*
11 Diamond ring Frenchman dropped in wild shrub (7) RHOMBUS {RH{0}{M}BUS*}
12 Study aspects of sex? Am in! Exciting!! (7) EXAMINE [T]
13 Kind to muffle — at the onset! — naughty nasal sound (5) SNORT {S{Na...y}ORT}
14 Circumstantially single man consumes bites of nutrients and proteins for energy (4,5) WIND POWER {WI{Nu...s}D{Pr...n}OWER}
16 Doctor cures poor father as expected (3,3,3,6) PAR FOR THE COURSE*
19 Was sorry about gluttony, having eaten two times (9) REGRETTED {RE}{GRE{T}{T}ED}
22 Headgear frequently sported backwards by American pilot (5) TIARA {AmeRicAn+pIloT}<=
24 The woman's oddly better with a drink (4,3) HERB TEA {HER}{BeTtEr}{A}
26 Strong feeling — two essentially divides (1+50×2)×2! (3,4) ILL WILL {tWo} in {1+LL}{1+LL}
27 Rise in geeks' demands? (5) NEEDS (RisE in NERDS)
28 Space program's final stages caught in new energy crisis (9) EMERGENCY {s..cE}{p...aM}{ERGEN{C}Y}*
DOWN
1 Garfunkel is wearing this man's suit (6) HEARTS {HE{ART}'S}
2 When it was time for action from Zorro, he texted you desperately! (4,4) ZERO HOUR {ZORRO+HE+U}*
3 Spiritual master gets ordinary student inspired by the endlessly fascinating journey (6,4) RABBIT HOLE {RABBI}{TH{O}{L}E}
4 Puzzle gossip involving Gussalufz getting extremely gross (6) JIGSAW {J{I}{GrosS}AW}
5 Old Indian coin is over 10 euros, they feel (8) ANTENNAE {ANN{TEN}A}{E}
6 A bit of ale serving as water (4) AQUA {Ale}{QUA}
7 Raised five children, now regularly hides to take stock (6) REVIEW {RaisEd+fiVe+chIldrEn+noW}
8 Prepare one for final journey, then hear sermon, taking veil off (8) ENHEARSE [T]
15 Hospital department to ask questions covering a month with zero record of performance (10) PROCTOLOGY {PR{OCT}{0}{LOG}Y}
17 One with some trust on god during complicated test finds concentration (8) TITRATES {T{1}{Tr..t}{RA}TES*}
18 Gangster breaks rules, switches allegiance (8) REALIGNS {RE{AL}IGNS}
20 Plot revealed by Imagine Dragons played in reverse (6) GARDEN [T<=]
21 Push liberal nonsense (6) DRIVEL {DRIVE}{L}
23 A lover not on top sets down cushions (6) ALLAYS {A}{Lo..r}{LAYS} Not on top? See comments
25 I am disappointed about a mission (4) T?S? (Addendum - TASK {T{A}SK} - See comments)
Reference List
Indian Railways = IR, Frenchman = M, About = RE, Time = T, 50 = L, Caught = C, Ordinary = O, Student = L, Old indian coin = ANNA, Euro =E, As = QUA, Record = LOG, God = RA, Gangster = AL(Capone), Liberal = L