I'm basing my answer on the article 江信江疑是什么意思 which gives a reasonable explanation.
It's a play on words. It begins with
half believing, half doubting / skeptical
The line 将信将疑 comes from the poem 吊古战场文 by Tang-dynasty poet 李华.
However the meme replaces 将 (jiāng) with the surname 江 (Jiāng) which has the same pronunciation and is ...