John 6:2

Verse

Καὶ ἠκολούθει αὐτῷ ὄχλος πολύς, ὅτι ἑώρων αὐτοῦ τὰ σημεῖα ἃ ἐποίει ἐπὶ τῶν ἀσθενούντων.

RBT Greek Interlinear:

190; ēkolouthei; ἠκολούθει; were following; V-IIA-3S

1161; de; δὲ; then; Conj

846; autō; αὐτῷ; to himself; PPro-DM3S

3793; ochlos; ὄχλος; Multitude; N-NMS

4183; polys; πολύς; great; Adj-NMS

3754; hoti; ὅτι; that; Conj

2334; etheōroun; ἐθεώρουν*; they were seeing; V-IIA-3P

3588; ta; τὰ; the ones; Art-ANP

4592; sēmeia; σημεῖα; signs; N-ANP

3739; ha; ἃ; the things that; RelPro-ANP

4160; epoiei; ἐποίει; was performing; V-IIA-3S

1909; epi; ἐπὶ; upon; Prep

3588; tōn; τῶν; the; Art-GMP

770; asthenountōn; ἀσθενούντων; those who are being weak; V-PPA-GMP

RBT Translation:

Now a great multitude was accompanying himself because they were looking attentively at the Signs whom he was making upon the basis of^73e those who are weak.

LITV Translation:
And a great crowd followed Him, for they saw His miracles which He did on the sick ones.

ESV Translation:
And a large crowd was following him, because they saw the signs that he was doing on the sick.

Footnotes

73e

Greek  ἐπὶ τῶν ἀσθενούντων. On the basis of those who are weak.

He is not performing miracles onto sick people, but making signs on account of sick people. τῶν ἀσθενούντων is in the genitive. The genitive of "upon" can be translated "on the basis of," "upon the grounds of," etc, depending on a variety of factors, especially the verb, and of course having the right context. ἐπὶ with a genitive is typically used of location or place, and various relations such as "dependence upon."

See Liddell-Scott for full lexigraphical definitions and usage on ἐπὶ