If you use an Energy Search and don't find any Basic Energy, can you then play another Energy Search even though you know it will fail?
Yes, you can search for energy cards even if you know you won't find them. They exist as legal cards, therefore they can be searched for.
Source: PUI Rules Team (2004-01-15), PUI Rules Team (2004-01-22)

Relevant cards

Note: All applicable cards may not be listed below.
BW1_93
BW7_128
DP1_117
DP5_90
EX1_90
EX10_94
EX14_86
SWSH1_161
SWSH1_161
TK1-Latias_9
TK1-Latios_9
TK2-Minun_9
TK2-Plusle_8
TK3-Lucario_8
WOTCE1_153
WOTCFO_59