Please could you help me to create a Latin motto which means ‘I am, therefore I thank.’ I’ve thought of sum ergo laudo, but perhaps laudo is closer to ‘I praise’. I’m looking for a word with a nuance closer to ‘I give thanks’ or ‘I am thankful’ but, because this is for a motto, I should like to capture the meaning of ‘I thank’ in a single Latin verb. Am I correct in thinking that the word order in the motto would be sum + ergo + (the word you suggest)? Thanks so much!
There is no Latin verb that means "thank". There is the noun "thank", gratia, and you can "give thanks", agere gratias. Using this, you'd get sum ergo gratias ago.
But this might sound a little clumsy, so using laudare (which is more "to praise" than "to thank") is a decent option. Whether you value simplicity or accuracy more is a matter of taste. With laudare you'd get sum ergo laudo as you suggest.
The other two answers focused on "to give thanks" part of your question, but neglect the other option you gave: "I am thankful." The latter allows for more possibilities, although I think the most straightforward would be:
Sum ergo gratiam habeo.
I am therefore I am thankful/grateful.
gratias agere is more active in nature, and really does mean something more like "I give thanks"; whereas gratiam habere is more about the state in which someone is, so "I am grateful." For a motto, I take it you want to express the fact that you are a grateful person, not that you go around saying thanks to everyone. For this reason, gratiam habere is better.
I can't think of a way to express this in a single word---there is no inherent reason why a language should be able to express something like this in a single word. Maybe you could poach a word from another language, like the Greek? There you could do:
sum ergo εὐχαριστῶ (eucharisto, whence the word 'Eucharist')
However, that doesn't make for a good motto outside of Classics/Biblical Studies circles.
bene facis, bene vocas, bene narras
Thus, you could say something like
sum ergo bene vocas
Later in the entry there is a suggestion bene alone can also be used, as also stated in the linked question.
PS: credit goes to the linked question for inspiration.