The best replacement for agnosia is aphasia.

The best alternatives to agnosia are rated as following:
★★★★★  aphasia
★★★  anosognosia
★★  apraxia
★  stereognosis
★  anomia
★  prosopagnosia

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Speaking about agnosia, one probably shouldn't forget about prosopagnosia.

Other search terms related to agnosia and their ratings are:
★★★★★ prosopagnosia
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Google Trends

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agnosia
aphasia
anosognosia