Requisite Knowledge by Elfman

This was a fairly straightforward puzzle from Elfman. It had the look of a letters latent puzzle, however the wordplay pointed to the entire word and the solver had to deduce the omitted letter by cross-checking. The letters omitted from answers, in clue order, spelt –

“I keep six honest serving men
They taught me all I knew”

This from The Elephant’s Child by Rudyard Kipling. The verse continues –

“Their names are What and Why and When
And How and Where and Who.”
Solvers had to highlight the six names placed symmetrically in the grid, thus determining the central letter as W.

1 Dramatic merchant loses nothing taking a female name (7)
ANTONIA ANTONIO (ref. The Merchant of Venice) less O + A
7 Cambodia and native Chinese destroyed region governed by prince (7)
KHANATE K + HAN + ATE (destroyed)
11 Romance around a smooth shoal produces the main chance (15, three words)
LOAVES AND FISHES A in LOVE + SAND (to smooth) + FISHES
12 Lines with vassal replacing Prince in Indic language (7)
ROMANES ROPES less P replaced with MAN (vassal)
13 Prime red coloured protective covering (8)
PERIDERM Anagram PRIME RED
14 Fish I found during mission in choppy sea (10)
SERRANIDAE Anagram SEA containing ERRAND
15 Hit low trajectory shot not caught sloping at end (6)
HIPPED CHIPPED less C (caught)
20 Army character that's Greek chief (8)
TAXIARCH TA (Territorial Army) + XI (Greek character) + ARCH (chief): & lit.
22 Gods flush out everything in vessel (7)
DISHFUL DI (gods) + Anagram FLUSH
23 Irish leaving in a plane behaved as before (6) 
ABORNE AIRBORNE less IR Irish
25 Go regularly to batten down hatches? (6)
ATTEND Hidden
26 Siren summoned when learner's in back (7)
DELILAH L (learner) in HAILED (reversed)
28 Cavalry accepting many a Frenchwoman (8)
HORTENSE TEN in HORSE
32 In addition, article reminiscent of the past's not right (7)
THERETO THE + RETRO less R
34 Disbanded soldiers from SA rode off (10)
REFORMADOS Anagram FROM SA RODE
37 Basic libation turned up unexpectedly in exotic tea (9, two words)
TABLE WINE Anagram TEA containing BLEW IN
38 Paris without sun and rain splashing about on the Rive Gauche? (8)
RIPARIAN Anagram PARI(S) + RAIN less S (sun)
39 Disastrous rains veiled sun and stellar system (14, two words) 
ISLAND UNIVERSE Anagram RAINS VEILED SUN
40 Elastic band found in watch (7)
SPRINGY RING in SPY
41 Something emitting a deep sound good for bass musical instrument (7)
GITTERN (B)ITTERN replacing B (bass) with G (god)
 
Down
1 Rule in land's acceptable yet less acceptable (7)
ALRIGHT R (rule) in ALIGHT The definition indicates that this is a less acceptable spelling of ALL RIGHT!
2 Athenian going north must exchange lira for marks in Greek province (5)
NOMOS SOLON reversed with M replacing L
3 Wild primates, higher than lower animal, show cooperative disposition (10, two words)
TEAM SPIRIT Anagram PRIMATES above IT
4 Legally substitute debts from tax missing on drug? (6)
NOVATE No VAT (therefore TAX missing) + E (drug)
5 Continuously but with difficulty (10, three words) 
AT A STRETCH 2 definitions
6 Take in bomb without top around what may be dynamite stick (6)
INHERE (m)INE containing HE (high explosive) + R (take)
7 Head dressed with dead tree and crowned with a wreath of ivy (9)
HEDERATED Anagram HEAD + D (dead) + TREE
8 What won't cuckoo do? I find little yen for building (6)
NIDIFY Anagram I FIND + Y (yen)
9 Tried to like juvenile delinquent (6)
TASTED T (to) + AS (like) + TED
10 Gypsy girl has in gem a ... (9)
ESMERALDA ‘S (has) in EMERALD + A
16 ... worthless distraction, an embedded stone containing black in gold (7)
PABULUM PLUM containing B in AU
17 Smoke a hundred and one fish (5)
CIGAR CI (101) + GAR
18 What follows baby confused Brit father (10)
AFTERBIRTH Anagram BRITFATHER
19 Plant producing resin discharging a not quite recently discovered hydrocarbon (6)
BUTENE BUTE(a) less A + NE (not)
21 Like foam up north - inclined to have mass instead of density (5)
REAMY READY replacing D (density) with M (mass)
23 Draw attention to queen taking time in counsel (9) 
ADVERTISE ER + T (time) in ADVISE
24 Depositing in secret screen (8)
HOARDING 2 definitions
27 In a rather wet way, smell's deadly? Not half with iodine inside! (7)
HUMIDLY HUM + (dea)DLY containing I (iodine)
29 What may take away damaged old English liner (7)
ELOINER Anagram OE LINER
30 Expose as a lie old European from the south being ancient Greek (6)
EOLIAN NAIL O E (reversed)
31 Tree growth from a knot in surface (6) 
OAKNUT A KN in OUT
33 High-flyer's using energy for power in object in orbit (6)
ELANET  E for P in PLANET
35 Magnetic flux density in antenna is not so strong (7)
FEEBLER B in FEELER
36 What may be found at the foreparts of haulers above water sailors employ (5)
HAWSES Initial letters Haulers Above Water Sailors Employ

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